diff --git a/.dart_tool/package_config.json b/.dart_tool/package_config.json
index f9c157edc0f..b6def050f3c 100644
--- a/.dart_tool/package_config.json
+++ b/.dart_tool/package_config.json
@@ -11,7 +11,7 @@
     "constraint, update this by running tools/generate_package_config.dart."
   ],
   "configVersion": 2,
-  "generated": "2021-09-07T14:56:54.026010",
+  "generated": "2021-09-01T12:41:37.776425",
   "generator": "tools/generate_package_config.dart",
   "packages": [
     {
@@ -761,7 +761,7 @@
       "name": "vm",
       "rootUri": "../pkg/vm",
       "packageUri": "lib/",
-      "languageVersion": "2.15"
+      "languageVersion": "2.12"
     },
     {
       "name": "vm_service",
diff --git a/pkg/vm/lib/transformations/type_flow/transformer.dart b/pkg/vm/lib/transformations/type_flow/transformer.dart
index 02f23ab3e0e..2ed3a8e9eaf 100644
--- a/pkg/vm/lib/transformations/type_flow/transformer.dart
+++ b/pkg/vm/lib/transformations/type_flow/transformer.dart
@@ -315,7 +315,13 @@ class AnnotateKernel extends RecursiveVisitor {
     Constant? constantValue;
     bool isInt = false;
 
-    final nullable = type is NullableType;
+    // Note: the explicit type `bool` is needed because the checked-in version
+    // of the CFE that we use for bootstrapping doesn't yet have constructor
+    // tearoffs enabled, and the fix for bug
+    // https://github.com/dart-lang/language/issues/1785 only takes effect when
+    // constructor tearoffs are enabled.  TODO(paulberry): remove the type after
+    // the bootstrap CFE enables constructor tearoffs.
+    final bool nullable = type is NullableType;
     if (nullable) {
       type = type.baseType;
     }
diff --git a/pkg/vm/pubspec.yaml b/pkg/vm/pubspec.yaml
index 9b70250bede..20b2cd728dd 100644
--- a/pkg/vm/pubspec.yaml
+++ b/pkg/vm/pubspec.yaml
@@ -4,7 +4,7 @@ description: VM specific Dart code and helper scripts
 publish_to: none
 
 environment:
-  sdk: '>=2.15.0 <3.0.0'
+  sdk: '>=2.12.0 <3.0.0'
 
 dependencies:
   args: ^1.4.4