diff --git a/mlir/lib/Transforms/Inliner.cpp b/mlir/lib/Transforms/Inliner.cpp
--- a/mlir/lib/Transforms/Inliner.cpp
+++ b/mlir/lib/Transforms/Inliner.cpp
@@ -745,9 +745,17 @@
 
   // Initialize the op specific pass pipelines.
   llvm::StringMap<OpPassManager> pipelines;
-  for (OpPassManager pipeline : opPipelineList)
-    if (!pipeline.empty())
-      pipelines.try_emplace(pipeline.getOpName(), pipeline);
+  for (OpPassManager pipeline : opPipelineList) {
+    if (pipeline.empty())
+      continue;
+    auto it = pipelines.try_emplace(pipeline.getOpName(), pipeline);
+    if (!it.second) {
+      llvm::errs()
+          << "Inliner: Registering duplicate simplification pipeline for op '"
+          << it.first->getKey() << "'\n";
+      return failure();
+    }
+  }
   opPipelines.assign({std::move(pipelines)});
 
   return success();
diff --git a/mlir/test/Transforms/inlining.mlir b/mlir/test/Transforms/inlining.mlir
--- a/mlir/test/Transforms/inlining.mlir
+++ b/mlir/test/Transforms/inlining.mlir
@@ -3,6 +3,9 @@
 // RUN: mlir-opt %s -inline='default-pipeline=''' -mlir-print-debuginfo -mlir-print-local-scope | FileCheck %s --check-prefix INLINE-LOC
 // RUN: mlir-opt %s -inline | FileCheck %s --check-prefix INLINE_SIMPLIFY
 // RUN: mlir-opt %s -inline='op-pipelines=func.func(canonicalize,cse)' | FileCheck %s --check-prefix INLINE_SIMPLIFY
+// RUN: not mlir-opt %s -inline='op-pipelines=func.func(canonicalize),func.func(cse)' 2>&1 | FileCheck %s --check-prefix ERROR_DUPLICATE_PIPELINE
+
+// ERROR_DUPLICATE_PIPELINE: Inliner: Registering duplicate simplification pipeline for op 'func.func'
 
 // Inline a function that takes an argument.
 func @func_with_arg(%c : i32) -> i32 {