diff --git a/api/handler/get.go b/api/handler/get.go
index c524dfc1..881edc13 100644
--- a/api/handler/get.go
+++ b/api/handler/get.go
@@ -291,17 +291,16 @@ func checkPreconditions(info *data.ObjectInfo, args *conditionalArgs, md5Enabled
 }
 
 func parseConditionalHeaders(headers http.Header) (*conditionalArgs, error) {
-	var err error
 	args := &conditionalArgs{
 		IfMatch:     data.UnQuote(headers.Get(api.IfMatch)),
 		IfNoneMatch: data.UnQuote(headers.Get(api.IfNoneMatch)),
 	}
 
-	if args.IfModifiedSince, err = parseHTTPTime(headers.Get(api.IfModifiedSince)); err != nil {
-		return nil, err
+	if httpTime, err := parseHTTPTime(headers.Get(api.IfModifiedSince)); err == nil {
+		args.IfModifiedSince = httpTime
 	}
-	if args.IfUnmodifiedSince, err = parseHTTPTime(headers.Get(api.IfUnmodifiedSince)); err != nil {
-		return nil, err
+	if httpTime, err := parseHTTPTime(headers.Get(api.IfUnmodifiedSince)); err == nil {
+		args.IfUnmodifiedSince = httpTime
 	}
 
 	return args, nil
diff --git a/api/handler/head_test.go b/api/handler/head_test.go
index 4eebc8c8..b6aec292 100644
--- a/api/handler/head_test.go
+++ b/api/handler/head_test.go
@@ -68,6 +68,16 @@ func TestConditionalHead(t *testing.T) {
 		api.IfModifiedSince: zeroTime.UTC().Format(http.TimeFormat),
 	}
 	headObject(t, tc, bktName, objName, headers, http.StatusNotModified)
+
+	headers = map[string]string{
+		api.IfUnmodifiedSince: zeroTime.UTC().Format(time.RFC3339), // invalid format, header is ignored
+	}
+	headObject(t, tc, bktName, objName, headers, http.StatusOK)
+
+	headers = map[string]string{
+		api.IfModifiedSince: objInfo.Created.Add(time.Minute).Format(time.RFC3339), // invalid format, header is ignored
+	}
+	headObject(t, tc, bktName, objName, headers, http.StatusOK)
 }
 
 func headObject(t *testing.T, tc *handlerContext, bktName, objName string, headers map[string]string, status int) {
diff --git a/api/handler/patch.go b/api/handler/patch.go
index a9e79bc6..fab7a157 100644
--- a/api/handler/patch.go
+++ b/api/handler/patch.go
@@ -138,13 +138,12 @@ func (h *handler) PatchObjectHandler(w http.ResponseWriter, r *http.Request) {
 }
 
 func parsePatchConditionalHeaders(headers http.Header) (*conditionalArgs, error) {
-	var err error
 	args := &conditionalArgs{
 		IfMatch: data.UnQuote(headers.Get(api.IfMatch)),
 	}
 
-	if args.IfUnmodifiedSince, err = parseHTTPTime(headers.Get(api.IfUnmodifiedSince)); err != nil {
-		return nil, err
+	if httpTime, err := parseHTTPTime(headers.Get(api.IfUnmodifiedSince)); err == nil {
+		args.IfUnmodifiedSince = httpTime
 	}
 
 	return args, nil
diff --git a/api/handler/patch_test.go b/api/handler/patch_test.go
index aa294230..33aa3393 100644
--- a/api/handler/patch_test.go
+++ b/api/handler/patch_test.go
@@ -60,6 +60,13 @@ func TestPatch(t *testing.T) {
 				api.IfMatch:           etag,
 			},
 		},
+		{
+			name: "If-Unmodified-Since invalid format, header is ignored",
+			rng:  "bytes 0-2/*",
+			headers: map[string]string{
+				api.IfUnmodifiedSince: created.Add(-24 * time.Hour).Format(time.RFC3339),
+			},
+		},
 		{
 			name: "invalid range syntax",
 			rng:  "bytes 0-2",