1 files changed, 5 insertions, 1 deletions
diff --git a/string.c b/string.c
index 0cadd61fe2..3dca59b6db 100644
--- a/string.c
+++ b/string.c
@@ -839,14 +839,18 @@ rb_str_index(str, sub, offset)
     VALUE str, sub;
     long offset;
 {
+    long pos;
+
     if (offset < 0) {
 	offset += RSTRING(str)->len;
 	if (offset < 0) return -1;
     }
     if (RSTRING(str)->len - offset < RSTRING(sub)->len) return -1;
     if (RSTRING(sub)->len == 0) return offset;
-    return rb_memsearch(RSTRING(sub)->ptr, RSTRING(sub)->len,
+    pos = rb_memsearch(RSTRING(sub)->ptr, RSTRING(sub)->len,
 			RSTRING(str)->ptr+offset, RSTRING(str)->len-offset);
+    if (pos < 0) return pos;
+    return pos + offset;
 }
 
 static VALUE