diff --git a/imageproxy.go b/imageproxy.go
index a52ad6f..dbb8a2d 100644
--- a/imageproxy.go
+++ b/imageproxy.go
@@ -275,7 +275,7 @@ func should304(req *http.Request, resp *http.Response) bool {
 	if err != nil {
 		return false
 	}
-	if lastModified.Before(ifModSince) {
+	if lastModified.Before(ifModSince) || lastModified.Equal(ifModSince) {
 		return true
 	}
 
diff --git a/imageproxy_test.go b/imageproxy_test.go
index 6a242c7..aa5878a 100644
--- a/imageproxy_test.go
+++ b/imageproxy_test.go
@@ -223,11 +223,16 @@ func TestShould304(t *testing.T) {
 			"HTTP/1.1 200 OK\nEtag: \"v\"\n\n",
 			true,
 		},
-		{ // last-modified match
+		{ // last-modified before
 			"GET / HTTP/1.1\nIf-Modified-Since: Sun, 02 Jan 2000 00:00:00 GMT\n\n",
 			"HTTP/1.1 200 OK\nLast-Modified: Sat, 01 Jan 2000 00:00:00 GMT\n\n",
 			true,
 		},
+		{ // last-modified match
+			"GET / HTTP/1.1\nIf-Modified-Since: Sat, 01 Jan 2000 00:00:00 GMT\n\n",
+			"HTTP/1.1 200 OK\nLast-Modified: Sat, 01 Jan 2000 00:00:00 GMT\n\n",
+			true,
+		},
 
 		// mismatches
 		{