diff --git a/source/opt/merge_return_pass.cpp b/source/opt/merge_return_pass.cpp
index c262ea073a..41734945e6 100644
--- a/source/opt/merge_return_pass.cpp
+++ b/source/opt/merge_return_pass.cpp
@@ -828,7 +828,8 @@ BasicBlock* MergeReturnPass::CreateContinueTarget(uint32_t header_label_id) {
 
 bool MergeReturnPass::CreateSingleCaseSwitch(BasicBlock* merge_target) {
   // Insert the switch before any code is run.  We have to split the entry
-  // block to make sure the OpVariable instructions remain in the entry block.
+  // block to make sure the OpVariable instructions and DebugFunctionDefinition
+  // instructions remain in the entry block.
   BasicBlock* start_block = &*function_->begin();
   auto split_pos = start_block->begin();
   while (split_pos->opcode() == spv::Op::OpVariable) {
@@ -838,6 +839,18 @@ bool MergeReturnPass::CreateSingleCaseSwitch(BasicBlock* merge_target) {
   BasicBlock* old_block =
       start_block->SplitBasicBlock(context(), TakeNextId(), split_pos);
 
+  // Find DebugFunctionDefinition inst in the old block, and if we can find it,
+  // move it to the entry block. Since DebugFunctionDefinition is not necessary
+  // after OpVariable inst, we have to traverse the whole block to find it.
+  for (auto pos = old_block->begin(); pos != old_block->end(); ++pos) {
+    if (pos->GetShader100DebugOpcode() ==
+        NonSemanticShaderDebugInfo100DebugFunctionDefinition) {
+      start_block->AddInstruction(MakeUnique<Instruction>(*pos));
+      pos.Erase();
+      break;
+    }
+  }
+
   // Add the switch to the end of the entry block.
   InstructionBuilder builder(
       context(), start_block,
diff --git a/test/opt/pass_merge_return_test.cpp b/test/opt/pass_merge_return_test.cpp
index 494f2e95f0..c005d748bc 100644
--- a/test/opt/pass_merge_return_test.cpp
+++ b/test/opt/pass_merge_return_test.cpp
@@ -2598,6 +2598,70 @@ TEST_F(MergeReturnPassTest, OverflowTest1) {
   EXPECT_EQ(Pass::Status::Failure, std::get<1>(result));
 }
 
+TEST_F(MergeReturnPassTest, DebugFunctionDefinitionStillInEntryBlock) {
+  // Make sure that the DebugFunctionDefinition instruction is still in the
+  // entry block
+  const std::string text =
+      R"(
+; CHECK: OpFunction
+; CHECK: OpLabel
+; CHECK: DebugFunctionDefinition
+; CHECK: OpSelectionMerge
+; CHECK: OpCompositeExtract
+; CHECK: OpUGreaterThan
+        OpCapability Shader
+        OpExtension "SPV_KHR_non_semantic_info"
+        %2 = OpExtInstImport "NonSemantic.Shader.DebugInfo.100"
+        OpMemoryModel Logical GLSL450
+        OpEntryPoint GLCompute %main "main" %entryPointParam_main %gl_GlobalInvocationID
+        %1 = OpString "test"
+        OpDecorate %gl_GlobalInvocationID BuiltIn GlobalInvocationId
+        OpDecorate %entryPointParam_main Location 0
+        %void = OpTypeVoid
+        %4 = OpExtInst %void %2 DebugSource %1
+        %uint = OpTypeInt 32 0
+        %uint_100 = OpConstant %uint 100
+        %uint_5 = OpConstant %uint 5
+        %uint_11 = OpConstant %uint 11
+        %10 = OpExtInst %void %2 DebugCompilationUnit %uint_100 %uint_5 %4 %uint_11
+        %12 = OpTypeFunction %void
+        %uint_0 = OpConstant %uint 0
+        %14 = OpExtInst %void %2 DebugTypeFunction %uint_0 %void
+        %uint_2 = OpConstant %uint 2
+        %16 = OpExtInst %void %2 DebugFunction %1 %14 %4 %uint_2 %uint_5 %10 %1 %uint_0 %uint_2
+        %v3uint = OpTypeVector %uint 3
+        %_ptr_Input_v3uint = OpTypePointer Input %v3uint
+        %bool = OpTypeBool
+        %uint_3 = OpConstant %uint 3
+        %int = OpTypeInt 32 1
+        %_ptr_Output_int = OpTypePointer Output %int
+        %int_1 = OpConstant %int 1
+        %int_0 = OpConstant %int 0
+        %gl_GlobalInvocationID = OpVariable %_ptr_Input_v3uint Input    ; BuiltIn GlobalInvocationId
+        %entryPointParam_main = OpVariable %_ptr_Output_int Output      ; Location 0
+
+        ; Function main
+        %main = OpFunction %void None %12
+        %13 = OpLabel
+        %20 = OpExtInst %void %2 DebugScope %16
+        %29 = OpLoad %v3uint %gl_GlobalInvocationID
+        %37 = OpCompositeExtract %uint %29 0
+        %39 = OpUGreaterThan %bool %37 %uint_3
+        %19 = OpExtInst %void %2 DebugFunctionDefinition %16 %main
+        OpSelectionMerge %21 None
+        OpBranchConditional %39 %23 %21
+        %21 = OpLabel
+        OpStore %entryPointParam_main %int_1
+        OpReturn
+        %23 = OpLabel
+        OpStore %entryPointParam_main %int_0
+        OpReturn
+        OpFunctionEnd
+)";
+
+  SinglePassRunAndMatch<MergeReturnPass>(text, true);
+}
+
 }  // namespace
 }  // namespace opt
 }  // namespace spvtools