diff --git a/flang/lib/Optimizer/CodeGen/CodeGen.cpp b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
--- a/flang/lib/Optimizer/CodeGen/CodeGen.cpp
+++ b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
@@ -706,6 +706,18 @@
   }
 };
 
+/// Convert `fir.end`
+struct FirEndOpConversion : public FIROpConversion<fir::FirEndOp> {
+  using FIROpConversion::FIROpConversion;
+
+  mlir::LogicalResult
+  matchAndRewrite(fir::FirEndOp firEnd, OpAdaptor,
+                  mlir::ConversionPatternRewriter &rewriter) const override {
+    return rewriter.notifyMatchFailure(
+        firEnd, "fir.end codegen is not implemented yet");
+  }
+};
+
 /// Lower `fir.has_value` operation to `llvm.return` operation.
 struct HasValueOpConversion : public FIROpConversion<fir::HasValueOp> {
   using FIROpConversion::FIROpConversion;
@@ -1592,19 +1604,20 @@
     mlir::OwningRewritePatternList pattern(context);
     pattern.insert<
         AbsentOpConversion, AddcOpConversion, AddrOfOpConversion,
-        AllocaOpConversion, BoxAddrOpConversion, BoxCharLenOpConversion, BoxDimsOpConversion,
-        BoxEleSizeOpConversion, BoxIsAllocOpConversion, BoxIsArrayOpConversion,
-        BoxIsPtrOpConversion, BoxRankOpConversion, CallOpConversion,
-        CmpcOpConversion, ConvertOpConversion, DispatchOpConversion,
-        DispatchTableOpConversion, DTEntryOpConversion, DivcOpConversion,
-        EmboxCharOpConversion, ExtractValueOpConversion, HasValueOpConversion,
-        GenTypeDescOpConversion, GlobalLenOpConversion, GlobalOpConversion,
-        InsertOnRangeOpConversion, InsertValueOpConversion,
-        IsPresentOpConversion, LoadOpConversion, NegcOpConversion,
-        MulcOpConversion, SelectCaseOpConversion, SelectOpConversion,
-        SelectRankOpConversion, SelectTypeOpConversion, StoreOpConversion,
-        SubcOpConversion, UnboxCharOpConversion, UndefOpConversion,
-        UnreachableOpConversion, ZeroOpConversion>(typeConverter);
+        AllocaOpConversion, BoxAddrOpConversion, BoxCharLenOpConversion,
+        BoxDimsOpConversion, BoxEleSizeOpConversion, BoxIsAllocOpConversion,
+        BoxIsArrayOpConversion, BoxIsPtrOpConversion, BoxRankOpConversion,
+        CallOpConversion, CmpcOpConversion, ConvertOpConversion,
+        DispatchOpConversion, DispatchTableOpConversion, DTEntryOpConversion,
+        DivcOpConversion, EmboxCharOpConversion, ExtractValueOpConversion,
+        FirEndOpConversion, HasValueOpConversion, GenTypeDescOpConversion,
+        GlobalLenOpConversion, GlobalOpConversion, InsertOnRangeOpConversion,
+        InsertValueOpConversion, IsPresentOpConversion, LoadOpConversion,
+        NegcOpConversion, MulcOpConversion, SelectCaseOpConversion,
+        SelectOpConversion, SelectRankOpConversion, SelectTypeOpConversion,
+        StoreOpConversion, SubcOpConversion, UnboxCharOpConversion,
+        UndefOpConversion, UnreachableOpConversion, ZeroOpConversion>(
+        typeConverter);
     mlir::populateStdToLLVMConversionPatterns(typeConverter, pattern);
     mlir::arith::populateArithmeticToLLVMConversionPatterns(typeConverter,
                                                             pattern);
diff --git a/flang/test/Fir/convert-to-llvm-invalid.fir b/flang/test/Fir/convert-to-llvm-invalid.fir
--- a/flang/test/Fir/convert-to-llvm-invalid.fir
+++ b/flang/test/Fir/convert-to-llvm-invalid.fir
@@ -93,3 +93,10 @@
   %0 = fir.gentypedesc !fir.type<derived3>
   return
 }
+
+// -----
+
+// Test `fir.end` conversion failure. Not implemented yet.
+
+// expected-error@+1{{failed to legalize operation 'fir.end'}}
+"fir.end"() : () -> ()