diff --git a/src/string.c b/src/string.c
index 5683920..407ea89 100644
--- a/src/string.c
+++ b/src/string.c
@@ -25,6 +25,7 @@
  */
 
 #include <stdlib.h>
+#include <stdint.h>
 #include <string.h>
 
 #include "object.h"
@@ -148,6 +149,28 @@ cfw_string_append(CFWString *str, CFWString *append)
 	return true;
 }
 
+size_t
+cfw_string_find(CFWString *str, CFWString *substr, cfw_range_t range)
+{
+	size_t i;
+
+	if (range.start > str->len)
+		return SIZE_MAX;
+
+	if (range.length == SIZE_MAX)
+		range.length = str->len - range.start;
+
+	if (range.start + range.length > str->len || substr->len > range.length)
+		return SIZE_MAX;
+
+	for (i = range.start; i <= range.start + range.length - substr->len;
+	    i++)
+		if (!memcmp(str->data + i, substr->data, substr->len))
+			return i;
+
+	return SIZE_MAX;
+}
+
 static CFWClass class = {
 	.name = "CFWString",
 	.size = sizeof(CFWString),
diff --git a/src/string.h b/src/string.h
index c53a7db..22c4ef4 100644
--- a/src/string.h
+++ b/src/string.h
@@ -28,6 +28,7 @@
 #define __COREFW_STRING_H__
 
 #include "class.h"
+#include "range.h"
 
 typedef struct CFWString CFWString;
 extern CFWClass *cfw_string;
@@ -35,5 +36,6 @@ extern const char* cfw_string_c(CFWString*);
 extern size_t cfw_string_len(CFWString*);
 extern bool cfw_string_set(CFWString*, const char*);
 extern bool cfw_string_append(CFWString*, CFWString*);
+extern size_t cfw_string_find(CFWString*, CFWString*, cfw_range_t);
 
 #endif
diff --git a/tests/tests.c b/tests/tests.c
index 8717477..9853353 100644
--- a/tests/tests.c
+++ b/tests/tests.c
@@ -56,6 +56,10 @@ main()
 
 	puts(cfw_string_c(s[0]));
 
+	s[1] = cfw_new(cfw_string, "ll");
+	printf("%zd\n", cfw_string_find(s[0], s[1], cfw_range_all));
+	cfw_unref(s[1]);
+
 	cfw_unref(s[0]);
 
 	return 0;