diff --git a/lib/c.zig b/lib/c.zig
index 30c6e0cd76e6b30c553d37a90cb8eb26451b8722..9df1b3fb01044bab1fcbf417ed406f75f47dd3b4 100644
--- a/lib/c.zig
+++ b/lib/c.zig
@@ -82,7 +82,7 @@ fn memset(dest: ?[*]u8, c: u8, len: usize) callconv(.C) ?[*]u8 {
         var d = dest.?;
         var n = len;
         while (true) {
-            d.* = c;
+            d[0] = c;
             n -= 1;
             if (n == 0) break;
             d += 1;
diff --git a/lib/std/os.zig b/lib/std/os.zig
index 578a8ddcbc8340d3ae13dbb130bae1fcc3e7f490..02ed710dd310de0fc91e5cec224c748dba646bf1 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -1868,7 +1868,7 @@ pub fn getenv(key: []const u8) ?[]const u8 {
         }
         // Search the entire `environ` because we don't have a null terminated pointer.
         var ptr = std.c.environ;
-        while (ptr.*) |line| : (ptr += 1) {
+        while (ptr[0]) |line| : (ptr += 1) {
             var line_i: usize = 0;
             while (line[line_i] != 0 and line[line_i] != '=') : (line_i += 1) {}
             const this_key = line[0..line_i];
diff --git a/lib/std/process.zig b/lib/std/process.zig
index 0b64b5910d8664d3b125b22f99e89d1277b279ba..dffd6b1701a262207edb4baa5298bda29fc6bd2e 100644
--- a/lib/std/process.zig
+++ b/lib/std/process.zig
@@ -313,7 +313,7 @@ pub fn getEnvMap(allocator: Allocator) !EnvMap {
         return result;
     } else if (builtin.link_libc) {
         var ptr = std.c.environ;
-        while (ptr.*) |line| : (ptr += 1) {
+        while (ptr[0]) |line| : (ptr += 1) {
             var line_i: usize = 0;
             while (line[line_i] != 0 and line[line_i] != '=') : (line_i += 1) {}
             const key = line[0..line_i];
diff --git a/src/AstGen.zig b/src/AstGen.zig
index c9abb1859ba9f5f2f6b25501bddd580848a9c6f8..870772831335e158a047f988269feca7c61a3f3e 100644
--- a/src/AstGen.zig
+++ b/src/AstGen.zig
@@ -812,6 +812,7 @@ fn expr(gz: *GenZir, scope: *Scope, rl: ResultLoc, node: Ast.Node.Index) InnerEr
 
         .deref => {
             const lhs = try expr(gz, scope, .none, node_datas[node].lhs);
+            _ = try gz.addUnTok(.validate_deref, lhs, main_tokens[node]);
             switch (rl) {
                 .ref => return lhs,
                 else => {
@@ -2500,6 +2501,7 @@ fn unusedResultExpr(gz: *GenZir, scope: *Scope, statement: Ast.Node.Index) Inner
             .memset,
             .validate_array_init_ty,
             .validate_struct_init_ty,
+            .validate_deref,
             => break :b true,
         }
     } else switch (maybe_unused_result) {
diff --git a/src/Sema.zig b/src/Sema.zig
index 30cebe18b339ff593f8965c5500cf4988d41aa0f..0e7188a6c9a5f1d7f41c5be3a035999968effae5 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -1080,6 +1080,11 @@ fn analyzeBodyInner(
                 i += 1;
                 continue;
             },
+            .validate_deref => {
+                try sema.zirValidateDeref(block, inst);
+                i += 1;
+                continue;
+            },
             .@"export" => {
                 try sema.zirExport(block, inst);
                 i += 1;
@@ -3849,6 +3854,28 @@ fn zirValidateArrayInit(
     }
 }
 
+fn zirValidateDeref(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void {
+    const inst_data = sema.code.instructions.items(.data)[inst].un_tok;
+    const src = inst_data.src();
+    const operand_src: LazySrcLoc = .{ .token_offset = inst_data.src_tok + 1 };
+    const operand = try sema.resolveInst(inst_data.operand);
+    const operand_ty = sema.typeOf(operand);
+
+    if (operand_ty.zigTypeTag() != .Pointer) {
+        return sema.fail(block, src, "cannot dereference non-pointer type '{}'", .{operand_ty.fmt(sema.mod)});
+    } else switch (operand_ty.ptrSize()) {
+        .One, .C => {},
+        .Many => return sema.fail(block, src, "index syntax required for unknown-length pointer type '{}'", .{operand_ty.fmt(sema.mod)}),
+        .Slice => return sema.fail(block, src, "index syntax required for slice type '{}'", .{operand_ty.fmt(sema.mod)}),
+    }
+
+    if (try sema.resolveMaybeUndefVal(block, operand_src, operand)) |val| {
+        if (val.isUndef()) {
+            return sema.fail(block, src, "cannot dereference undefined value", .{});
+        }
+    }
+}
+
 fn failWithBadMemberAccess(
     sema: *Sema,
     block: *Block,
diff --git a/src/Zir.zig b/src/Zir.zig
index e6acfe8ed2aac7135fb630650decbac52226a4fe..26bb09860d8f0ad2f5ec1a01137b6cb3eb7626a9 100644
--- a/src/Zir.zig
+++ b/src/Zir.zig
@@ -729,6 +729,9 @@ pub const Inst = struct {
         /// Same as `validate_array_init` but additionally communicates that the
         /// resulting array initialization value is within a comptime scope.
         validate_array_init_comptime,
+        /// Check that operand type supports the dereference operand (.*).
+        /// Uses the `un_tok` field.
+        validate_deref,
         /// A struct literal with a specified type, with no fields.
         /// Uses the `un_node` field.
         struct_init_empty,
@@ -1156,6 +1159,7 @@ pub const Inst = struct {
                 .validate_struct_init_comptime,
                 .validate_array_init,
                 .validate_array_init_comptime,
+                .validate_deref,
                 .struct_init_empty,
                 .struct_init,
                 .struct_init_ref,
@@ -1309,6 +1313,7 @@ pub const Inst = struct {
                 .validate_struct_init_comptime,
                 .validate_array_init,
                 .validate_array_init_comptime,
+                .validate_deref,
                 .@"export",
                 .export_value,
                 .set_cold,
@@ -1709,6 +1714,7 @@ pub const Inst = struct {
                 .validate_struct_init_comptime = .pl_node,
                 .validate_array_init = .pl_node,
                 .validate_array_init_comptime = .pl_node,
+                .validate_deref = .un_tok,
                 .struct_init_empty = .un_node,
                 .field_type = .pl_node,
                 .field_type_ref = .pl_node,
diff --git a/src/print_zir.zig b/src/print_zir.zig
index 480a3e2a4fa19f02a2c492983480e684beb42b53..fe8446b34acf7feb5563bed168ba0a298ac16f5d 100644
--- a/src/print_zir.zig
+++ b/src/print_zir.zig
@@ -242,6 +242,7 @@ const Writer = struct {
             .ret_tok,
             .ensure_err_payload_void,
             .closure_capture,
+            .validate_deref,
             => try self.writeUnTok(stream, inst),
 
             .bool_br_and,
diff --git a/test/cases/compile_errors/assign_to_invalid_dereference.zig b/test/cases/compile_errors/assign_to_invalid_dereference.zig
new file mode 100644
index 0000000000000000000000000000000000000000..cb35004034d7dbc2f9145782758cb157937bea47
--- /dev/null
+++ b/test/cases/compile_errors/assign_to_invalid_dereference.zig
@@ -0,0 +1,9 @@
+export fn entry() void {
+    'a'.* = 1;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :2:8: error: cannot dereference non-pointer type 'comptime_int'
diff --git a/test/cases/compile_errors/deref_on_undefined_value.zig b/test/cases/compile_errors/deref_on_undefined_value.zig
new file mode 100644
index 0000000000000000000000000000000000000000..fa12e2824cad3e1794a6d1bad893d4d8f8198af6
--- /dev/null
+++ b/test/cases/compile_errors/deref_on_undefined_value.zig
@@ -0,0 +1,10 @@
+comptime {
+    var a: *u8 = undefined;
+    _ = a.*;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:10: error: cannot dereference undefined value
diff --git a/test/cases/compile_errors/deref_slice_and_get_len_field.zig b/test/cases/compile_errors/deref_slice_and_get_len_field.zig
new file mode 100644
index 0000000000000000000000000000000000000000..1ba03c6d50cf90ad0c647ec3552f24fb0d5bcc5e
--- /dev/null
+++ b/test/cases/compile_errors/deref_slice_and_get_len_field.zig
@@ -0,0 +1,10 @@
+export fn entry() void {
+    var a: []u8 = undefined;
+    _ = a.*.len;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:10: error: index syntax required for slice type '[]u8'
diff --git a/test/cases/compile_errors/dereference_an_array.zig b/test/cases/compile_errors/dereference_an_array.zig
new file mode 100644
index 0000000000000000000000000000000000000000..f5aabf081c5a6c6d59668ff2d65362244f179d10
--- /dev/null
+++ b/test/cases/compile_errors/dereference_an_array.zig
@@ -0,0 +1,14 @@
+var s_buffer: [10]u8 = undefined;
+pub fn pass(in: []u8) []u8 {
+    var out = &s_buffer;
+    out.*.* = in[0];
+    return out.*[0..1];
+}
+
+export fn entry() usize { return @sizeOf(@TypeOf(&pass)); }
+
+// error
+// backend=stage2
+// target=native
+//
+// :4:10: error: cannot dereference non-pointer type '[10]u8'
diff --git a/test/cases/compile_errors/dereference_slice.zig b/test/cases/compile_errors/dereference_slice.zig
new file mode 100644
index 0000000000000000000000000000000000000000..7dba3b55d82272bfddc925ca0dbfa586f1952f1e
--- /dev/null
+++ b/test/cases/compile_errors/dereference_slice.zig
@@ -0,0 +1,12 @@
+fn entry(x: []i32) i32 {
+    return x.*;
+}
+comptime {
+    _ = entry;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :2:13: error: index syntax required for slice type '[]i32'
diff --git a/test/cases/compile_errors/dereference_unknown_length_pointer.zig b/test/cases/compile_errors/dereference_unknown_length_pointer.zig
new file mode 100644
index 0000000000000000000000000000000000000000..353f94b8d9cb682a55e3b7d2ac72da2201737928
--- /dev/null
+++ b/test/cases/compile_errors/dereference_unknown_length_pointer.zig
@@ -0,0 +1,9 @@
+export fn entry(x: [*]i32) i32 {
+    return x.*;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :2:13: error: index syntax required for unknown-length pointer type '[*]i32'
diff --git a/test/cases/compile_errors/invalid_deref_on_switch_target.zig b/test/cases/compile_errors/invalid_deref_on_switch_target.zig
new file mode 100644
index 0000000000000000000000000000000000000000..a880b16fca8579d4cf982582834aa3c349a31857
--- /dev/null
+++ b/test/cases/compile_errors/invalid_deref_on_switch_target.zig
@@ -0,0 +1,17 @@
+comptime {
+    var tile = Tile.Empty;
+    switch (tile.*) {
+        Tile.Empty => {},
+        Tile.Filled => {},
+    }
+}
+const Tile = enum {
+    Empty,
+    Filled,
+};
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:17: error: cannot dereference non-pointer type 'tmp.Tile'
diff --git a/test/cases/compile_errors/invalid_multiple_dereferences.zig b/test/cases/compile_errors/invalid_multiple_dereferences.zig
new file mode 100644
index 0000000000000000000000000000000000000000..3edebf7b1f79383e73e669bae0f1f82ccc13a00c
--- /dev/null
+++ b/test/cases/compile_errors/invalid_multiple_dereferences.zig
@@ -0,0 +1,19 @@
+export fn a() void {
+    var box = Box{ .field = 0 };
+    box.*.field = 1;
+}
+export fn b() void {
+    var box = Box{ .field = 0 };
+    var boxPtr = &box;
+    boxPtr.*.*.field = 1;
+}
+pub const Box = struct {
+    field: i32,
+};
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:8: error: cannot dereference non-pointer type 'tmp.Box'
+// :8:13: error: cannot dereference non-pointer type 'tmp.Box'
diff --git a/test/cases/compile_errors/stage1/comptime_ptrcast_of_zero-sized_type.zig b/test/cases/compile_errors/stage1/comptime_ptrcast_of_zero-sized_type.zig
new file mode 100644
index 0000000000000000000000000000000000000000..231e735cfa4d58e356123505bb6c8f7134146963
--- /dev/null
+++ b/test/cases/compile_errors/stage1/comptime_ptrcast_of_zero-sized_type.zig
@@ -0,0 +1,12 @@
+fn foo() void {
+    const node: struct {} = undefined;
+    const vla_ptr = @ptrCast([*]const u8, &node);
+    _ = vla_ptr;
+}
+comptime { foo(); }
+
+// error
+// backend=stage1
+// target=native
+//
+// tmp.zig:3:21: error: '*const struct:2:17' and '[*]const u8' do not have the same in-memory representation
diff --git a/test/cases/compile_errors/stage1/deref_on_undefined_value.zig b/test/cases/compile_errors/stage1/deref_on_undefined_value.zig
deleted file mode 100644
index f64d567a26c242685a23f91fb3752134f97b4940..0000000000000000000000000000000000000000
--- a/test/cases/compile_errors/stage1/deref_on_undefined_value.zig
+++ /dev/null
@@ -1,10 +0,0 @@
-comptime {
-    var a: *u8 = undefined;
-    _ = a.*;
-}
-
-// error
-// backend=stage1
-// target=native
-//
-// tmp.zig:3:9: error: attempt to dereference undefined value
diff --git a/test/cases/compile_errors/stage1/obj/assign_to_invalid_dereference.zig b/test/cases/compile_errors/stage1/obj/assign_to_invalid_dereference.zig
deleted file mode 100644
index 7fef5db83c33e930d40686158e122b081a9c9121..0000000000000000000000000000000000000000
--- a/test/cases/compile_errors/stage1/obj/assign_to_invalid_dereference.zig
+++ /dev/null
@@ -1,9 +0,0 @@
-export fn entry() void {
-    'a'.* = 1;
-}
-
-// error
-// backend=stage1
-// target=native
-//
-// tmp.zig:2:8: error: attempt to dereference non-pointer type 'comptime_int'
diff --git a/test/cases/compile_errors/stage1/obj/comptime_ptrcast_of_zero-sized_type.zig b/test/cases/compile_errors/stage1/obj/comptime_ptrcast_of_zero-sized_type.zig
deleted file mode 100644
index 231e735cfa4d58e356123505bb6c8f7134146963..0000000000000000000000000000000000000000
--- a/test/cases/compile_errors/stage1/obj/comptime_ptrcast_of_zero-sized_type.zig
+++ /dev/null
@@ -1,12 +0,0 @@
-fn foo() void {
-    const node: struct {} = undefined;
-    const vla_ptr = @ptrCast([*]const u8, &node);
-    _ = vla_ptr;
-}
-comptime { foo(); }
-
-// error
-// backend=stage1
-// target=native
-//
-// tmp.zig:3:21: error: '*const struct:2:17' and '[*]const u8' do not have the same in-memory representation
diff --git a/test/cases/compile_errors/stage1/obj/deref_slice_and_get_len_field.zig b/test/cases/compile_errors/stage1/obj/deref_slice_and_get_len_field.zig
deleted file mode 100644
index 98097597cc8f4db61359dd8b2751a63edd4c3dd0..0000000000000000000000000000000000000000
--- a/test/cases/compile_errors/stage1/obj/deref_slice_and_get_len_field.zig
+++ /dev/null
@@ -1,10 +0,0 @@
-export fn entry() void {
-    var a: []u8 = undefined;
-    _ = a.*.len;
-}
-
-// error
-// backend=stage1
-// target=native
-//
-// tmp.zig:3:10: error: attempt to dereference non-pointer type '[]u8'
diff --git a/test/cases/compile_errors/stage1/obj/dereference_an_array.zig b/test/cases/compile_errors/stage1/obj/dereference_an_array.zig
deleted file mode 100644
index 0dd91f70e53aa347ea69ddd58c570dc119e0aa65..0000000000000000000000000000000000000000
--- a/test/cases/compile_errors/stage1/obj/dereference_an_array.zig
+++ /dev/null
@@ -1,14 +0,0 @@
-var s_buffer: [10]u8 = undefined;
-pub fn pass(in: []u8) []u8 {
-    var out = &s_buffer;
-    out.*.* = in[0];
-    return out.*[0..1];
-}
-
-export fn entry() usize { return @sizeOf(@TypeOf(pass)); }
-
-// error
-// backend=stage1
-// target=native
-//
-// tmp.zig:4:10: error: attempt to dereference non-pointer type '[10]u8'
diff --git a/test/cases/compile_errors/stage1/obj/dereference_unknown_length_pointer.zig b/test/cases/compile_errors/stage1/obj/dereference_unknown_length_pointer.zig
deleted file mode 100644
index c305e4bc98abcae6029bd64f708e8ecf2b022a5b..0000000000000000000000000000000000000000
--- a/test/cases/compile_errors/stage1/obj/dereference_unknown_length_pointer.zig
+++ /dev/null
@@ -1,9 +0,0 @@
-export fn entry(x: [*]i32) i32 {
-    return x.*;
-}
-
-// error
-// backend=stage1
-// target=native
-//
-// tmp.zig:2:13: error: index syntax required for unknown-length pointer type '[*]i32'
diff --git a/test/cases/compile_errors/stage1/obj/invalid_deref_on_switch_target.zig b/test/cases/compile_errors/stage1/obj/invalid_deref_on_switch_target.zig
deleted file mode 100644
index 966a881543304a501d5a9f5b0db62d93e9caa65d..0000000000000000000000000000000000000000
--- a/test/cases/compile_errors/stage1/obj/invalid_deref_on_switch_target.zig
+++ /dev/null
@@ -1,17 +0,0 @@
-comptime {
-    var tile = Tile.Empty;
-    switch (tile.*) {
-        Tile.Empty => {},
-        Tile.Filled => {},
-    }
-}
-const Tile = enum {
-    Empty,
-    Filled,
-};
-
-// error
-// backend=stage1
-// target=native
-//
-// tmp.zig:3:17: error: attempt to dereference non-pointer type 'Tile'
diff --git a/test/cases/compile_errors/stage1/obj/invalid_multiple_dereferences.zig b/test/cases/compile_errors/stage1/obj/invalid_multiple_dereferences.zig
deleted file mode 100644
index f8a0b8013f0ccbaa8e1519cf013932b0ce607a18..0000000000000000000000000000000000000000
--- a/test/cases/compile_errors/stage1/obj/invalid_multiple_dereferences.zig
+++ /dev/null
@@ -1,19 +0,0 @@
-export fn a() void {
-    var box = Box{ .field = 0 };
-    box.*.field = 1;
-}
-export fn b() void {
-    var box = Box{ .field = 0 };
-    var boxPtr = &box;
-    boxPtr.*.*.field = 1;
-}
-pub const Box = struct {
-    field: i32,
-};
-
-// error
-// backend=stage1
-// target=native
-//
-// tmp.zig:3:8: error: attempt to dereference non-pointer type 'Box'
-// tmp.zig:8:13: error: attempt to dereference non-pointer type 'Box'
diff --git a/test/cases/compile_errors/stage1/obj/take_slice_of_invalid_dereference.zig b/test/cases/compile_errors/stage1/obj/take_slice_of_invalid_dereference.zig
deleted file mode 100644
index c039be373778354fee485a624a66d1e34aade8c6..0000000000000000000000000000000000000000
--- a/test/cases/compile_errors/stage1/obj/take_slice_of_invalid_dereference.zig
+++ /dev/null
@@ -1,10 +0,0 @@
-export fn entry() void {
-    const x = 'a'.*[0..];
-    _ = x;
-}
-
-// error
-// backend=stage1
-// target=native
-//
-// tmp.zig:2:18: error: attempt to dereference non-pointer type 'comptime_int'
diff --git a/test/cases/compile_errors/take_slice_of_invalid_dereference.zig b/test/cases/compile_errors/take_slice_of_invalid_dereference.zig
new file mode 100644
index 0000000000000000000000000000000000000000..35c1b2de0da4822b4ac2111251aab21cdf4bd256
--- /dev/null
+++ b/test/cases/compile_errors/take_slice_of_invalid_dereference.zig
@@ -0,0 +1,10 @@
+export fn entry() void {
+    const x = 'a'.*[0..];
+    _ = x;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :2:18: error: cannot dereference non-pointer type 'comptime_int'