diff --git a/mlir/lib/Transforms/Utils/RegionUtils.cpp b/mlir/lib/Transforms/Utils/RegionUtils.cpp
--- a/mlir/lib/Transforms/Utils/RegionUtils.cpp
+++ b/mlir/lib/Transforms/Utils/RegionUtils.cpp
@@ -497,6 +497,9 @@
       Value rhsOperand = rhsOperands[operand];
       if (lhsOperand == rhsOperand)
         continue;
+      // Check that the types of the operands match.
+      if (lhsOperand.getType() != rhsOperand.getType())
+        return failure();
 
       // Check that these uses are both external, or both internal.
       bool lhsIsInBlock = lhsOperand.getParentBlock() == leaderBlock;
diff --git a/mlir/test/Transforms/canonicalize-block-merge.mlir b/mlir/test/Transforms/canonicalize-block-merge.mlir
--- a/mlir/test/Transforms/canonicalize-block-merge.mlir
+++ b/mlir/test/Transforms/canonicalize-block-merge.mlir
@@ -202,3 +202,25 @@
 
   return
 }
+
+// Check that blocks are not merged if the types of the operands differ.
+
+// CHECK-LABEL: func @mismatch_operand_types(
+func @mismatch_operand_types(%arg0 : i1, %arg1 : memref<i32>, %arg2 : memref<i1>) {
+  %c0_i32 = constant 0 : i32
+  %true = constant true
+  br ^bb1
+
+^bb1:
+  cond_br %arg0, ^bb2, ^bb3
+
+^bb2:
+  // CHECK: store %{{.*}}, %{{.*}} : memref<i32>
+  store %c0_i32, %arg1[] : memref<i32>
+  br ^bb1
+
+^bb3:
+  // CHECK: store %{{.*}}, %{{.*}} : memref<i1>
+  store %true, %arg2[] : memref<i1>
+  br ^bb1
+}