diff --git a/test/standalone/config_header/autoconf_at/autoconf_at.txt b/test/standalone/config_header/autoconf_at/autoconf_at.txt
index fccd1255f887c410c0f86a87d51e531685a4382b..e35cb5f822ab889e727d0fd13fe263fedb8b24cd 100644
--- a/test/standalone/config_header/autoconf_at/autoconf_at.txt
+++ b/test/standalone/config_header/autoconf_at/autoconf_at.txt
@@ -35,3 +35,15 @@ what is 6*7? 42!
 @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
index 8dfbab96d7b4483305352787cc32e420f606f0db..77d15622e8223e3e51ccc66889deb2b0d79b563b 100644
--- a/test/standalone/config_header/autoconf_at/autoconf_at.txt.in
+++ b/test/standalone/config_header/autoconf_at/autoconf_at.txt.in
@@ -34,3 +34,15 @@ what is 6*7? @integer@!
 @@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/autoconf_undef/config.h b/test/standalone/config_header/autoconf_undef/config.h
index ef5b4abab30499feb5c82019ae8750e82b059512..3a649b0aca5576d75099906310d28ef049d50f4a 100644
--- a/test/standalone/config_header/autoconf_undef/config.h
+++ b/test/standalone/config_header/autoconf_undef/config.h
@@ -20,4 +20,15 @@ int foo();
 /* #undef PREFIX_TAB */
 /* #undef POSTFIX_SPACE */
 /* #undef POSTFIX_TAB */
+
+// #undef with underscored variable name
+#define SOME_UNDERSCORED 1
+
+// #undef with extra tokens after variable name (ignored)
+#define SOME_ONE 1
+
+// non-#undef # lines pass through unchanged
+#define KEPT_DEFINE value
+#include <kept.h>
 // TODO: unexpected newline is being added here
+
diff --git a/test/standalone/config_header/autoconf_undef/config.h.in b/test/standalone/config_header/autoconf_undef/config.h.in
index fafc3587658162eaae0c918320df9752b779086d..1a13ccf319a85432ff04916ac0145b23bf78a7d3 100644
--- a/test/standalone/config_header/autoconf_undef/config.h.in
+++ b/test/standalone/config_header/autoconf_undef/config.h.in
@@ -17,6 +17,16 @@ int foo();
 
 #undef PREFIX_SPACE
 #undef	PREFIX_TAB
-#undef POSTFIX_SPACE 
-#undef POSTFIX_TAB	
-// TODO: unexpected newline is being added here
\ No newline at end of file
+#undef POSTFIX_SPACE
+#undef POSTFIX_TAB
+
+// #undef with underscored variable name
+#undef SOME_UNDERSCORED
+
+// #undef with extra tokens after variable name (ignored)
+#undef SOME_ONE extra ignored tokens
+
+// non-#undef # lines pass through unchanged
+#define KEPT_DEFINE value
+#include <kept.h>
+// TODO: unexpected newline is being added here
diff --git a/test/standalone/config_header/build.zig b/test/standalone/config_header/build.zig
index e6d62557e223abb8e610cc945986ee82165fe14f..42080a0996c2b330a73ff5ad721be8a3d120e15b 100644
--- a/test/standalone/config_header/build.zig
+++ b/test/standalone/config_header/build.zig
@@ -21,6 +21,8 @@ pub fn build(b: *std.Build) void {
             .PREFIX_TAB = null,
             .POSTFIX_SPACE = null,
             .POSTFIX_TAB = null,
+
+            .SOME_UNDERSCORED = true,
         },
     );
     const check_config_header = b.addCheckFile(config_header.getOutputFile(), .{
@@ -37,6 +39,9 @@ pub fn build(b: *std.Build) void {
             .integer = 42,
             .string = "text",
             .string_at = "@string@",
+
+            .underscored_var = "value",
+            .at_sign = "@",
         },
     );
     const check_config_header_autoconf_at = b.addCheckFile(config_header_autoconf_at.getOutputFile(), .{