diff --git a/libc/include/__llvm-libc-common.h b/libc/include/__llvm-libc-common.h
index a0fa506c01ab..212e3c6a9446 100644
--- a/libc/include/__llvm-libc-common.h
+++ b/libc/include/__llvm-libc-common.h
@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC_COMMON_H
-#define LLVM_LIBC_COMMON_H
+#ifndef _LLVM_LIBC_COMMON_H
+#define _LLVM_LIBC_COMMON_H
 
 #define __LLVM_LIBC__ 1
 
@@ -87,4 +87,4 @@
 
 #endif // __cplusplus
 
-#endif // LLVM_LIBC_COMMON_H
+#endif // _LLVM_LIBC_COMMON_H
diff --git a/libc/utils/hdrgen/header.py b/libc/utils/hdrgen/header.py
index 9ea9f98f8fc8..42a075c4b6c8 100644
--- a/libc/utils/hdrgen/header.py
+++ b/libc/utils/hdrgen/header.py
@@ -124,7 +124,7 @@ class HeaderFile:
         }
 
     def header_guard(self):
-        return "LLVM_LIBC_" + "_".join(
+        return "_LLVM_LIBC_" + "_".join(
             word.upper() for word in NONIDENTIFIER.split(self.name) if word
         )
 
diff --git a/libc/utils/hdrgen/tests/expected_output/subdir/test.h b/libc/utils/hdrgen/tests/expected_output/subdir/test.h
index 20bab502e682..40936bcfcba6 100644
--- a/libc/utils/hdrgen/tests/expected_output/subdir/test.h
+++ b/libc/utils/hdrgen/tests/expected_output/subdir/test.h
@@ -6,8 +6,8 @@
 //
 //===---------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC_SUBDIR_TEST_H
-#define LLVM_LIBC_SUBDIR_TEST_H
+#ifndef _LLVM_LIBC_SUBDIR_TEST_H
+#define _LLVM_LIBC_SUBDIR_TEST_H
 
 #include "../__llvm-libc-common.h"
 #include "../llvm-libc-types/type_a.h"
@@ -23,4 +23,4 @@ int *ptrfunc(void) __NOEXCEPT;
 
 __END_C_DECLS
 
-#endif // LLVM_LIBC_SUBDIR_TEST_H
+#endif // _LLVM_LIBC_SUBDIR_TEST_H