diff --git a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
index a98e7276bef80..82d06e2b9eb55 100644
--- a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
+++ b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
@@ -107,7 +107,7 @@ function(_get_compile_options_from_config output_var)
   endif()
 
   if(LIBC_CONF_ERRNO_MODE)
-    set(APPEND config_options "-DLIBC_ERRNO_MODE=${LIBC_CONF_ERRNO_MODE}")
+    list(APPEND config_options "-DLIBC_ERRNO_MODE=${LIBC_CONF_ERRNO_MODE}")
   endif()
 
   set(${output_var} ${config_options} PARENT_SCOPE)