diff --git a/include/llvm-dialects/TableGen/Dialects.h b/include/llvm-dialects/TableGen/Dialects.h
index f4b6067..2328d51 100644
--- a/include/llvm-dialects/TableGen/Dialects.h
+++ b/include/llvm-dialects/TableGen/Dialects.h
@@ -21,6 +21,7 @@
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/StringMap.h"
 
 namespace llvm {
 class DagInit;
@@ -47,10 +48,11 @@ class GenDialect {
   std::string cppNamespace;
   std::vector<DialectType *> types;
   std::vector<OpClass *> opClasses;
+  llvm::StringMap<unsigned> operationCounts;
   std::vector<std::unique_ptr<Operation>> operations;
 
 public:
-  void finalize();
+  void finalize(llvm::raw_ostream &errs);
 
   llvm::ArrayRef<std::vector<Trait *>> attribute_lists() const {
     return m_attributeLists;
diff --git a/lib/TableGen/Dialects.cpp b/lib/TableGen/Dialects.cpp
index 6339066..3a9a4dd 100644
--- a/lib/TableGen/Dialects.cpp
+++ b/lib/TableGen/Dialects.cpp
@@ -28,7 +28,7 @@
 using namespace llvm;
 using namespace llvm_dialects;
 
-void GenDialect::finalize() {
+void GenDialect::finalize(raw_ostream &errs) {
   // Build the list of different attribute lists.
   auto traitLess = [](Trait *lhs, Trait *rhs) {
     return lhs->getName() < rhs->getName();
@@ -41,6 +41,18 @@ void GenDialect::finalize() {
 
   std::vector<Operation *> traitOperations;
 
+  bool hasDuplicates = false;
+  for (const auto &[op, count] : operationCounts) {
+    if (count != 1) {
+      errs << "Found op with non-unique mnemonic: " << op << '\n';
+      hasDuplicates = true;
+    }
+  }
+
+  if (hasDuplicates)
+    report_fatal_error(
+        "Aborting dialect generation since non-unique mnemonics were found!");
+
   for (const auto &op : operations) {
     if (op->traits.empty())
       continue;
@@ -219,5 +231,5 @@ void GenDialectsContext::init(RecordKeeper &records,
   }
 
   for (auto &dialectEntry : m_dialects)
-    dialectEntry.second->finalize();
+    dialectEntry.second->finalize(llvm::errs());
 }
diff --git a/lib/TableGen/Operations.cpp b/lib/TableGen/Operations.cpp
index dbbc502..0ee493a 100644
--- a/lib/TableGen/Operations.cpp
+++ b/lib/TableGen/Operations.cpp
@@ -447,6 +447,7 @@ bool Operation::parse(raw_ostream &errs, GenDialectsContext *context,
 
   op->m_builders.push_back(std::move(builder));
 
+  ++dialect->operationCounts[op->mnemonic];
   dialect->operations.push_back(std::move(op));
 
   return true;
diff --git a/test/tablegen/duplicate-ops.td b/test/tablegen/duplicate-ops.td
new file mode 100644
index 0000000..101c505
--- /dev/null
+++ b/test/tablegen/duplicate-ops.td
@@ -0,0 +1,45 @@
+// RUN: not --crash llvm-dialects-tblgen -gen-dialect-defs -dialect=dups -I%S/../../include %s 2>&1 | FileCheck --check-prefixes=CHECK %s
+
+// CHECK:      Found op with non-unique mnemonic: duplicate.op
+// CHECK-NEXT: Found op with non-unique mnemonic: duplicate.op.1
+// CHECK-NEXT: LLVM ERROR: Aborting dialect generation since non-unique mnemonics were found! 
+
+include "llvm-dialects/Dialect/Dialect.td"
+
+def TestDialect : Dialect {
+  let name = "dups";
+  let cppNamespace = "dups";
+}
+
+class TestOp<string mnemonic_, list<Trait> traits_>
+    : Op<TestDialect, mnemonic_, traits_>;
+
+def DuplicateOp : TestOp<"duplicate.op",
+                       []> {
+  let results = (outs);
+  let arguments = (ins);
+}
+
+def DuplicateOp1 : TestOp<"duplicate.op",
+                       []> {
+  let results = (outs);
+  let arguments = (ins);
+}
+
+def DuplicateOp2 : TestOp<"duplicate.op.1",
+                       []> {
+  let results = (outs);
+  let arguments = (ins);
+}
+
+def DuplicateOp3 : TestOp<"duplicate.op.1",
+                       []> {
+  let results = (outs);
+  let arguments = (ins);
+}
+
+def UniqueOp : TestOp<"unique.op",
+                       []> {
+  let results = (outs);
+  let arguments = (ins);
+}