diff --git a/mlir/include/mlir/IR/OpDefinition.h b/mlir/include/mlir/IR/OpDefinition.h
--- a/mlir/include/mlir/IR/OpDefinition.h
+++ b/mlir/include/mlir/IR/OpDefinition.h
@@ -725,6 +725,14 @@
   result_type_range getResultTypes() {
     return this->getOperation()->getResultTypes();
   }
+
+  /// Sets the types of all results to `types`.
+  ///
+  /// Requires that the number of elements of `types` matches the number of
+  /// results.
+  void setResultTypes(TypeRange types) {
+    this->getOperation()->setResultTypes(types);
+  }
 };
 } // end namespace detail
 
diff --git a/mlir/include/mlir/IR/Operation.h b/mlir/include/mlir/IR/Operation.h
--- a/mlir/include/mlir/IR/Operation.h
+++ b/mlir/include/mlir/IR/Operation.h
@@ -292,6 +292,12 @@
   result_type_iterator result_type_end() { return getResultTypes().end(); }
   result_type_range getResultTypes();
 
+  /// Sets the types of all results to `types`.
+  ///
+  /// Requires that the number of elements of `types` matches the number of
+  /// results.
+  void setResultTypes(TypeRange types) { getResults().setTypes(types); }
+
   //===--------------------------------------------------------------------===//
   // Attributes
   //===--------------------------------------------------------------------===//
diff --git a/mlir/include/mlir/IR/OperationSupport.h b/mlir/include/mlir/IR/OperationSupport.h
--- a/mlir/include/mlir/IR/OperationSupport.h
+++ b/mlir/include/mlir/IR/OperationSupport.h
@@ -735,6 +735,11 @@
   using type_range = ArrayRef<Type>;
   type_range getTypes() const;
   auto getType() const { return getTypes(); }
+  /// Sets the types of values in this range to the given `types`.
+  ///
+  /// Requires that the number of elements of `types` matches the number of
+  /// elements in this range.
+  void setTypes(TypeRange types);
 
 private:
   /// See `llvm::indexed_accessor_range` for details.
diff --git a/mlir/lib/Dialect/SCF/Transforms/StructuralTypeConversions.cpp b/mlir/lib/Dialect/SCF/Transforms/StructuralTypeConversions.cpp
--- a/mlir/lib/Dialect/SCF/Transforms/StructuralTypeConversions.cpp
+++ b/mlir/lib/Dialect/SCF/Transforms/StructuralTypeConversions.cpp
@@ -31,8 +31,7 @@
       newResultTypes.push_back(newType);
     }
     rewriter.updateRootInPlace(op, [&] {
-      for (auto t : llvm::zip(op.getResults(), newResultTypes))
-        std::get<0>(t).setType(std::get<1>(t));
+      op.setResultTypes(newResultTypes);
       auto bodyArgs = op.getBody()->getArguments();
       for (auto t : llvm::zip(llvm::drop_begin(bodyArgs, 1), newResultTypes))
         std::get<0>(t).setType(std::get<1>(t));
@@ -49,6 +48,16 @@
   LogicalResult
   matchAndRewrite(IfOp op, ArrayRef<Value> operands,
                   ConversionPatternRewriter &rewriter) const override {
+    // TODO: Generalize this to any type conversion, not just 1:1.
+    //
+    // We need to implement something more sophisticated here that tracks which
+    // types convert to which other types and does the appropriate
+    // materialization logic.
+    // For example, it's possible that one result type converts to 0 types and
+    // another to 2 types, so newResultTypes would at least be the right size to
+    // not crash in the setResultTypes call, but then we would set the the wrong
+    // type on the SSA values! These edge cases are also why we cannot safely
+    // use the TypeConverter::convertTypes helper here.
     SmallVector<Type, 6> newResultTypes;
     for (auto type : op.getResultTypes()) {
       Type newType = typeConverter->convertType(type);
@@ -56,10 +65,7 @@
         return rewriter.notifyMatchFailure(op, "not a 1:1 type conversion");
       newResultTypes.push_back(newType);
     }
-    rewriter.updateRootInPlace(op, [&] {
-      for (auto t : llvm::zip(op.getResults(), newResultTypes))
-        std::get<0>(t).setType(std::get<1>(t));
-    });
+    rewriter.updateRootInPlace(op, [&] { op.setResultTypes(newResultTypes); });
     return success();
   }
 };
diff --git a/mlir/lib/IR/OperationSupport.cpp b/mlir/lib/IR/OperationSupport.cpp
--- a/mlir/lib/IR/OperationSupport.cpp
+++ b/mlir/lib/IR/OperationSupport.cpp
@@ -478,6 +478,12 @@
   return getBase()->getResultTypes().slice(getStartIndex(), size());
 }
 
+void ResultRange::setTypes(TypeRange types) {
+  assert(types.size() == size() && "mismatch in number of types!");
+  for (auto t : llvm::zip(*this, types))
+    std::get<0>(t).setType(std::get<1>(t));
+}
+
 /// See `llvm::indexed_accessor_range` for details.
 OpResult ResultRange::dereference(Operation *op, ptrdiff_t index) {
   return op->getResult(index);