diff --git a/src/Sema.zig b/src/Sema.zig
index b59159cbf28a09c3940ae6267840032f8dfbabe8..c3abfcd422e84002153603b71c3ad7e927fc73cb 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -379,7 +379,7 @@ pub const Block = struct {
     /// pop the error trace upon block exit.
     error_return_trace_index: Air.Inst.Ref = .none,
 
-    /// when null, it is determined by build mode, changed by @setRuntimeSafety
+    /// when null, it is determined by the owner modules build mode, changed by @setRuntimeSafety
     want_safety: ?bool = null,
 
     /// What mode to generate float operations in, set by @setFloatMode
@@ -532,7 +532,7 @@ pub const Block = struct {
     }
 
     fn wantSafeTypes(block: *const Block) bool {
-        return block.want_safety orelse switch (block.sema.pt.zcu.optimizeMode()) {
+        return block.want_safety orelse switch (block.ownerModule().optimize_mode) {
             .Debug => true,
             .ReleaseSafe => true,
             .ReleaseFast => false,
@@ -542,7 +542,7 @@ pub const Block = struct {
 
     fn wantSafety(block: *const Block) bool {
         if (block.isComptime()) return false; // runtime safety checks are pointless in comptime blocks
-        return block.want_safety orelse switch (block.sema.pt.zcu.optimizeMode()) {
+        return block.want_safety orelse switch (block.ownerModule().optimize_mode) {
             .Debug => true,
             .ReleaseSafe => true,
             .ReleaseFast => false,
diff --git a/src/Zcu.zig b/src/Zcu.zig
index 7060dfaec4c6159c773029b7f0b213b7970df306..3e5b9a6e8f00431b864df14d9b6da9c976a1e893 100644
--- a/src/Zcu.zig
+++ b/src/Zcu.zig
@@ -3908,13 +3908,6 @@ pub fn getTarget(zcu: *const Zcu) *const Target {
     return &zcu.root_mod.resolved_target.result;
 }
 
-/// Deprecated. There is no global optimization mode for a Zig Compilation
-/// Unit. Instead, look up the optimization mode based on the Module that
-/// contains the source code being analyzed.
-pub fn optimizeMode(zcu: *const Zcu) std.builtin.OptimizeMode {
-    return zcu.root_mod.optimize_mode;
-}
-
 pub fn handleUpdateExports(
     zcu: *Zcu,
     export_indices: []const Export.Index,
diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index 885ca0aa1c9eb33540dae5e4a18c9cf1f7112222..4eec8b49a0ae6349208e84ee7fa6809b73520745 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -445,7 +445,7 @@ pub const Function = struct {
     }
 
     fn wantSafety(f: *Function) bool {
-        return switch (f.dg.pt.zcu.optimizeMode()) {
+        return switch (f.dg.mod.optimize_mode) {
             .Debug, .ReleaseSafe => true,
             .ReleaseFast, .ReleaseSmall => false,
         };
@@ -1301,7 +1301,7 @@ pub const DeclGen = struct {
             else => .initializer,
         };
 
-        const safety_on = switch (zcu.optimizeMode()) {
+        const safety_on = switch (dg.mod.optimize_mode) {
             .Debug, .ReleaseSafe => true,
             .ReleaseFast, .ReleaseSmall => false,
         };