diff --git a/str.h b/str.h
index a0f0229..973ef9e 100644
--- a/str.h
+++ b/str.h
@@ -27,8 +27,13 @@ extern int str_diff(const char *a,const char *b) __pure__;
  * limit characters match. */
 extern int str_diffn(const char *a,const char *b,unsigned int limit) __pure__;
 
+#ifdef __dietlibc__
+#include <string.h>
+#define str_len(foo) strlen(foo)
+#else
 /* str_len returns the index of \0 in s */
 extern unsigned int str_len(const char *s) __pure__;
+#endif
 
 /* str_chr returns the index of the first occurance of needle or \0 in haystack */
 extern unsigned int str_chr(const char *haystack,char needle) __pure__;
diff --git a/str/str_len.c b/str/str_len.c
index c1f1638..85f52dd 100644
--- a/str/str_len.c
+++ b/str/str_len.c
@@ -1,6 +1,7 @@
 #include "str.h"
 
 #ifdef __dietlibc__
+#undef str_len
 unsigned int str_len(const char* in) __attribute__((alias("strlen")));
 #else
 unsigned int str_len(const char* in) {