diff --git a/c-programming/strings/str_replace.h b/c-programming/strings/str_replace.h
index 5cef608..6a04c69 100644
--- a/c-programming/strings/str_replace.h
+++ b/c-programming/strings/str_replace.h
@@ -5,6 +5,9 @@
  * License: Unlicense
  */
 
+#ifndef _STR_REPLACE_H
+#define _STR_REPLACE_H
+
 #include <stdlib.h>
 #include <string.h>
 
@@ -16,3 +19,5 @@ char* str_replace(
   const char* replacement,
   ssize_t max_count
 );
+
+#endif /* _STR_REPLACE_H */