diff --git a/test/standalone/config_header/autoconf_at/autoconf_at.h b/test/standalone/config_header/autoconf_at/autoconf_at.h
new file mode 100644
index 0000000000000000000000000000000000000000..a4bdeff7af89c8b3c8b14d19abfae016692a2249
--- /dev/null
+++ b/test/standalone/config_header/autoconf_at/autoconf_at.h
@@ -0,0 +1,63 @@
+/* This file was generated by ConfigHeader using the Zig Build System. */
+/* Some Comment */
+int foo();
+// empty strings are preserved
+
+// line with misc content is preserved
+#define KEPT_VALUE no substitution
+
+// empty @ sigils are preserved
+#define AT_SIGIL_1 @
+#define AT_SIGIL_2 @@
+#define AT_SIGIL_3 @@@
+#define AT_SIGIL_4 @@@@
+
+// simple substitution
+#define SIMPLE_UNDEFINED 
+#define SIMPLE_DEFINED 
+#define SIMPLE_BOOL_TRUE 1
+#define SIMPLE_BOOL_FALSE 0
+#define SIMPLE_INTEGER 42
+#define SIMPLE_STRING text
+
+// double packed substitution
+#define DOUBLE_PACKED texttext
+
+// triple packed substitution
+#define TRIPLE_PACKED text42text
+
+// double separated substitution
+#define DOUBLE_SEPARATED 42.42
+
+// triple separated substitution
+#define TRIPLE_SEPARATED 42.1.42
+
+// misc prefix is preserved
+#define MISC_PREFIX false is 0
+
+// misc suffix is preserved
+#define MISC_SUFFIX 1 is true
+
+// surrounding content is preserved
+#define SURROUNDING what is 6*7? 42!
+
+// incomplete key is preserved
+#define INCOMPLETE_KEY @undefined
+
+// @-vars resolved only when they wrap valid characters, otherwise considered literals
+#define DOUBLE_WRAPPED @text@
+
+// expanded variables are considered strings after expansion
+#define EXPANDED_STRING @string@
+
+// variable name with underscores
+#define UNDERSCORED_VAR value
+
+// backslash before at-sigil does not prevent resolution
+#define BACKSLASH_AT \text
+
+// value that is an at-sign itself
+#define AT_SIGN_VALUE @
+
+// incomplete key mid-line is preserved, trailing content kept
+#define INCOMPLETE_MID @incomplete trailing content
diff --git a/test/standalone/config_header/autoconf_at/autoconf_at.h.in b/test/standalone/config_header/autoconf_at/autoconf_at.h.in
new file mode 100644
index 0000000000000000000000000000000000000000..3c7967a61eba0ba3e2276cd19eedf12bb466f118
--- /dev/null
+++ b/test/standalone/config_header/autoconf_at/autoconf_at.h.in
@@ -0,0 +1,62 @@
+/* Some Comment */
+int foo();
+// empty strings are preserved
+
+// line with misc content is preserved
+#define KEPT_VALUE no substitution
+
+// empty @ sigils are preserved
+#define AT_SIGIL_1 @
+#define AT_SIGIL_2 @@
+#define AT_SIGIL_3 @@@
+#define AT_SIGIL_4 @@@@
+
+// simple substitution
+#define SIMPLE_UNDEFINED @undefined@
+#define SIMPLE_DEFINED @defined@
+#define SIMPLE_BOOL_TRUE @boolean_true@
+#define SIMPLE_BOOL_FALSE @boolean_false@
+#define SIMPLE_INTEGER @integer@
+#define SIMPLE_STRING @string@
+
+// double packed substitution
+#define DOUBLE_PACKED @string@@string@
+
+// triple packed substitution
+#define TRIPLE_PACKED @string@@integer@@string@
+
+// double separated substitution
+#define DOUBLE_SEPARATED @integer@.@integer@
+
+// triple separated substitution
+#define TRIPLE_SEPARATED @integer@.@boolean_true@.@integer@
+
+// misc prefix is preserved
+#define MISC_PREFIX false is @boolean_false@
+
+// misc suffix is preserved
+#define MISC_SUFFIX @boolean_true@ is true
+
+// surrounding content is preserved
+#define SURROUNDING what is 6*7? @integer@!
+
+// incomplete key is preserved
+#define INCOMPLETE_KEY @undefined
+
+// @-vars resolved only when they wrap valid characters, otherwise considered literals
+#define DOUBLE_WRAPPED @@string@@
+
+// expanded variables are considered strings after expansion
+#define EXPANDED_STRING @string_at@
+
+// variable name with underscores
+#define UNDERSCORED_VAR @underscored_var@
+
+// backslash before at-sigil does not prevent resolution
+#define BACKSLASH_AT \@string@
+
+// value that is an at-sign itself
+#define AT_SIGN_VALUE @at_sign@
+
+// incomplete key mid-line is preserved, trailing content kept
+#define INCOMPLETE_MID @incomplete trailing content
diff --git a/test/standalone/config_header/autoconf_at/autoconf_at.txt b/test/standalone/config_header/autoconf_at/autoconf_at.txt
deleted file mode 100644
index e35cb5f822ab889e727d0fd13fe263fedb8b24cd..0000000000000000000000000000000000000000
--- a/test/standalone/config_header/autoconf_at/autoconf_at.txt
+++ /dev/null
@@ -1,49 +0,0 @@
-/* This file was generated by ConfigHeader using the Zig Build System. */
-// empty strings are preserved
-
-// line with misc content is preserved
-no substitution
-// empty @ sigils are preserved
-@
-@@
-@@@
-@@@@
-// simple substitution
-
-
-1
-0
-42
-text
-// double packed substitution
-texttext
-// triple packed substitution
-text42text
-// double separated substitution
-42.42
-// triple separated substitution
-42.1.42
-// misc prefix is preserved
-false is 0
-// misc suffix is preserved
-1 is true
-// surrounding content is preserved
-what is 6*7? 42!
-// incomplete key is preserved
-@undefined
-// @-vars resolved only when they wrap valid characters, otherwise considered literals
-@text@
-// expanded variables are considered strings after expansion
-@string@
-
-// variable name with underscores
-value
-
-// backslash before at-sigil does not prevent resolution
-\text
-
-// value that is an at-sign itself
-@
-
-// incomplete key mid-line is preserved, trailing content kept
-@incomplete trailing content
diff --git a/test/standalone/config_header/autoconf_at/autoconf_at.txt.in b/test/standalone/config_header/autoconf_at/autoconf_at.txt.in
deleted file mode 100644
index 77d15622e8223e3e51ccc66889deb2b0d79b563b..0000000000000000000000000000000000000000
--- a/test/standalone/config_header/autoconf_at/autoconf_at.txt.in
+++ /dev/null
@@ -1,48 +0,0 @@
-// empty strings are preserved
-
-// line with misc content is preserved
-no substitution
-// empty @ sigils are preserved
-@
-@@
-@@@
-@@@@
-// simple substitution
-@undefined@
-@defined@
-@boolean_true@
-@boolean_false@
-@integer@
-@string@
-// double packed substitution
-@string@@string@
-// triple packed substitution
-@string@@integer@@string@
-// double separated substitution
-@integer@.@integer@
-// triple separated substitution
-@integer@.@boolean_true@.@integer@
-// misc prefix is preserved
-false is @boolean_false@
-// misc suffix is preserved
-@boolean_true@ is true
-// surrounding content is preserved
-what is 6*7? @integer@!
-// incomplete key is preserved
-@undefined
-// @-vars resolved only when they wrap valid characters, otherwise considered literals
-@@string@@
-// expanded variables are considered strings after expansion
-@string_at@
-
-// variable name with underscores
-@underscored_var@
-
-// backslash before at-sigil does not prevent resolution
-\@string@
-
-// value that is an at-sign itself
-@at_sign@
-
-// incomplete key mid-line is preserved, trailing content kept
-@incomplete trailing content
diff --git a/test/standalone/config_header/build.zig b/test/standalone/config_header/build.zig
index 95daf60c28ea3aa5032377c7cb5c14f082a622a9..84439ba34cd7d97ae6cef9c9df99e2e0e9df5cd3 100644
--- a/test/standalone/config_header/build.zig
+++ b/test/standalone/config_header/build.zig
@@ -30,7 +30,7 @@ pub fn build(b: *std.Build) void {
     });
 
     const config_header_autoconf_at = b.addConfigHeader(
-        .{ .style = .{ .autoconf_at = b.path("autoconf_at/autoconf_at.txt.in") } },
+        .{ .style = .{ .autoconf_at = b.path("autoconf_at/autoconf_at.h.in") } },
         .{
             .undefined = null,
             .defined = {},
@@ -45,7 +45,7 @@ pub fn build(b: *std.Build) void {
         },
     );
     const check_config_header_autoconf_at = b.addCheckFile(config_header_autoconf_at.getOutputFile(), .{
-        .expected_exact = @embedFile("autoconf_at/autoconf_at.txt"),
+        .expected_exact = @embedFile("autoconf_at/autoconf_at.h"),
     });
 
     test_step.dependOn(&check_config_header.step);