diff --git a/jerry-core/vm/vm.c b/jerry-core/vm/vm.c
index f969746c2..decc02116 100644
--- a/jerry-core/vm/vm.c
+++ b/jerry-core/vm/vm.c
@@ -808,7 +808,8 @@ vm_loop (vm_frame_ctx_t *frame_ctx_p) /**< frame context */
           }
           default:
           {
-            JERRY_ASSERT (CBC_BRANCH_OFFSET_LENGTH (opcode) == 2);
+            JERRY_ASSERT (CBC_BRANCH_OFFSET_LENGTH (opcode) == 2
+                          || CBC_BRANCH_OFFSET_LENGTH (opcode) == 3);
 
             branch_offset <<= 8;
             branch_offset |= *(byte_code_p++);
diff --git a/tests/jerry/regression-test-issue-1555.js b/tests/jerry/regression-test-issue-1555.js
new file mode 100644
index 000000000..c277bfaf3
--- /dev/null
+++ b/tests/jerry/regression-test-issue-1555.js
@@ -0,0 +1,21 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+var src = "var a = 0; while(a) { switch(a) {";
+/* The += operation has a longer opcode. */
+for (var i = 0; i < 4000; i++)
+    src += "case " + i + ": a += a += a; break; ";
+src += "} }";
+
+eval(src);