diff --git a/src/include/string.h b/src/include/string.h
index dc301ea..30d014a 100644
--- a/src/include/string.h
+++ b/src/include/string.h
@@ -20,8 +20,8 @@
 char *strcpy(char *dst, const char *src);
 int strcmp(const char *s1, const char *s2);
 int strncmp(const char *s1, const char *s2, size_t maxlen);
-int strspn(const char *str, const char *spn);
-int strcspn(const char *str, const char *spn);
+size_t strspn(const char *str, const char *spn);
+size_t strcspn(const char *str, const char *spn);
 char *strstr(const char *haystack, const char *needle);
 char *strtok_r(char *str, const char *delim, char **ptr);
 char *strtok(char *str, const char *delim);
diff --git a/src/lib/string.c b/src/lib/string.c
index 7553295..b1996ff 100644
--- a/src/lib/string.c
+++ b/src/lib/string.c
@@ -125,9 +125,9 @@
 	return 0;
 }
 
-int strspn(const char *str, const char *spn)
+size_t strspn(const char *str, const char *spn)
 {
-	int ret = 0;
+	size_t ret = 0;
 
 	while (*str != 0) {
 		const char *p;
@@ -140,9 +140,9 @@
 	return ret;
 }
 
-int strcspn(const char *str, const char *spn)
+size_t strcspn(const char *str, const char *spn)
 {
-	int ret = 0;
+	size_t ret = 0;
 
 	while (*str != 0) {
 		const char *p;