diff --git a/include/util.h b/include/util.h
index f9f5c4e58..118988d0d 100644
--- a/include/util.h
+++ b/include/util.h
@@ -76,7 +76,7 @@ void halt(void) NORETURN;
 void memzero(void *s, unsigned long n);
 void *memset(void *s, unsigned long c, unsigned long n);
 void *memcpy(void* ptr_dst, const void* ptr_src, unsigned long n);
-int strncmp(const char *s1, const char *s2, int n);
+int PURE strncmp(const char *s1, const char *s2, int n);
 long CONST char_to_long(char c);
 long PURE str_to_long(const char* str);
 
diff --git a/src/util.c b/src/util.c
index 269111fe9..bbc8bf47f 100644
--- a/src/util.c
+++ b/src/util.c
@@ -79,7 +79,7 @@ memcpy(void* ptr_dst, const void* ptr_src, unsigned long n)
     return ptr_dst;
 }
 
-int
+int PURE
 strncmp(const char* s1, const char* s2, int n)
 {
     word_t i;