diff --git a/Tests/LibRegex/Regex.cpp b/Tests/LibRegex/Regex.cpp
index 7c4dfe80fe..7dbf8c6d3d 100644
--- a/Tests/LibRegex/Regex.cpp
+++ b/Tests/LibRegex/Regex.cpp
@@ -923,6 +923,8 @@ TEST_CASE(optimizer_atomic_groups)
         Tuple { "(a|)"sv, ""sv, true },                   // Ensure that empty alternatives are not outright removed
         Tuple { "a{2,3}|a{5,8}"sv, "abc"sv, false },      // Optimizer should not mess up the instruction stream by ignoring inter-insn dependencies, see #11247.
         Tuple { "^(a{2,3}|a{5,8})$"sv, "aaaa"sv, false }, // Optimizer should not mess up the instruction stream by ignoring inter-insn dependencies, see #11247.
+        // Optimizer should not chop off *half* of an instruction when fusing instructions.
+        Tuple { "cubic-bezier\\(\\s*(-?\\d+\\.?\\d*|-?\\.\\d+)\\s*,\\s*(-?\\d+\\.?\\d*|-?\\.\\d+)\\s*,\\s*(-?\\d+\\.?\\d*|-?\\.\\d+)\\s*,\\s*(-?\\d+\\.?\\d*|-?\\.\\d+)\\s*\\)"sv, "cubic-bezier(.05, 0, 0, 1)"sv, true },
         // ForkReplace shouldn't be applied where it would change the semantics
         Tuple { "(1+)\\1"sv, "11"sv, true },
         Tuple { "(1+)1"sv, "11"sv, true },
diff --git a/Userland/Libraries/LibRegex/RegexOptimizer.cpp b/Userland/Libraries/LibRegex/RegexOptimizer.cpp
index 8dd7335463..969f37143c 100644
--- a/Userland/Libraries/LibRegex/RegexOptimizer.cpp
+++ b/Userland/Libraries/LibRegex/RegexOptimizer.cpp
@@ -484,7 +484,12 @@ void Optimizer::append_alternation(ByteCode& target, ByteCode&& left, ByteCode&&
         if (left.spans().slice(left_block.start, left_end - left_block.start) != right.spans().slice(right_block.start, right_end - right_block.start))
             break;
 
-        left_skip = left_end;
+        state.instruction_position = 0;
+        while (state.instruction_position < left_end) {
+            auto& opcode = left.get_opcode(state);
+            left_skip = state.instruction_position;
+            state.instruction_position += opcode.size();
+        }
     }
 
     dbgln_if(REGEX_DEBUG, "Skipping {}/{} bytecode entries from {}/{}", left_skip, 0, left.size(), right.size());