diff --git a/pkg/analyzer/lib/src/fasta/ast_builder.dart b/pkg/analyzer/lib/src/fasta/ast_builder.dart
index c40153a2214..acccfc36aee 100644
--- a/pkg/analyzer/lib/src/fasta/ast_builder.dart
+++ b/pkg/analyzer/lib/src/fasta/ast_builder.dart
@@ -2142,14 +2142,13 @@ class AstBuilder extends StackListener {
 
     // Peek to leave type parameters on top of stack.
     List<TypeParameter> typeParameters = peek();
-    TypeParameter typeParameter = typeParameters[index];
-    typeParameter
-      ..extendsKeyword = extendsOrSuper
-      ..bound = bound;
 
-    if (typeParameter is TypeParameterImpl) {
-      typeParameter.varianceKeyword = variance;
-    }
+    // TODO (kallentu) : Clean up TypeParameterImpl casting once variance is
+    // added to the interface.
+    (typeParameters[index] as TypeParameterImpl)
+      ..extendsKeyword = extendsOrSuper
+      ..bound = bound
+      ..varianceKeyword = variance;
   }
 
   @override
diff --git a/pkg/analyzer/lib/src/generated/type_system.dart b/pkg/analyzer/lib/src/generated/type_system.dart
index 1b841ecaff4..8ff916677d4 100644
--- a/pkg/analyzer/lib/src/generated/type_system.dart
+++ b/pkg/analyzer/lib/src/generated/type_system.dart
@@ -1117,15 +1117,14 @@ class Dart2TypeSystem extends TypeSystem {
         DartType t1 = tArgs1[i];
         DartType t2 = tArgs2[i];
 
-        // TODO (kallentu) : Clean up TypeParameterElementImpl checks and
-        // casting once variance is added to the interface.
-        TypeParameterElement parameterElement = tParams[i];
-        Variance variance = Variance.covariant;
-        if (parameterElement is TypeParameterElementImpl) {
-          variance = parameterElement.variance;
-        }
-
-        if (variance.isContravariant) {
+        // TODO (kallentu) : Clean up TypeParameterElementImpl casting once
+        // variance is added to the interface.
+        Variance variance = (tParams[i] as TypeParameterElementImpl).variance;
+        if (variance.isCovariant) {
+          if (!isSubtypeOf(t1, t2)) {
+            return false;
+          }
+        } else if (variance.isContravariant) {
           if (!isSubtypeOf(t2, t1)) {
             return false;
           }
@@ -1134,9 +1133,8 @@ class Dart2TypeSystem extends TypeSystem {
             return false;
           }
         } else {
-          if (!isSubtypeOf(t1, t2)) {
-            return false;
-          }
+          throw new StateError('Type parameter ${tParams[i]} has unknown '
+              'variance $variance for subtype checking.');
         }
       }
       return true;
@@ -2173,15 +2171,13 @@ class InterfaceLeastUpperBoundHelper {
 
       var args = List<DartType>(args1.length);
       for (int i = 0; i < args1.length; i++) {
-        // TODO (kallentu) : Clean up TypeParameterElementImpl checks and
-        // casting once variance is added to the interface.
-        TypeParameterElement parameter = params[i];
-        Variance parameterVariance = Variance.covariant;
-        if (parameter is TypeParameterElementImpl) {
-          parameterVariance = parameter.variance;
-        }
-
-        if (parameterVariance.isContravariant) {
+        // TODO (kallentu) : Clean up TypeParameterElementImpl casting once
+        // variance is added to the interface.
+        Variance parameterVariance =
+            (params[i] as TypeParameterElementImpl).variance;
+        if (parameterVariance.isCovariant) {
+          args[i] = typeSystem.getLeastUpperBound(args1[i], args2[i]);
+        } else if (parameterVariance.isContravariant) {
           if (typeSystem is Dart2TypeSystem) {
             args[i] = (typeSystem as Dart2TypeSystem)
                 .getGreatestLowerBound(args1[i], args2[i]);
@@ -2201,7 +2197,8 @@ class InterfaceLeastUpperBoundHelper {
           //  parameters.
           args[i] = args1[i];
         } else {
-          args[i] = typeSystem.getLeastUpperBound(args1[i], args2[i]);
+          throw new StateError('Type parameter ${params[i]} has unknown '
+              'variance $parameterVariance for bounds calculation.');
         }
       }
 
diff --git a/pkg/analyzer/test/src/dart/element/subtype_test.dart b/pkg/analyzer/test/src/dart/element/subtype_test.dart
index 354f34e90f1..8d7b391e3f8 100644
--- a/pkg/analyzer/test/src/dart/element/subtype_test.dart
+++ b/pkg/analyzer/test/src/dart/element/subtype_test.dart
@@ -2846,7 +2846,7 @@ class SubtypeTest extends _SubtypingTestBase {
     );
   }
 
-  test_interfaceType_covariant_01() {
+  test_interfaceType_covariant() {
     var T = typeParameter('T', variance: Variance.covariant);
     var A = class_(name: 'A', typeParameters: [T]);
 
@@ -2861,22 +2861,11 @@ class SubtypeTest extends _SubtypingTestBase {
     );
 
     isSubtype(A_int, A_num, strT0: "A<int>", strT1: "A<num>");
+    isSubtype(A_num, A_num, strT0: "A<num>", strT1: "A<num>");
     isNotSubtype(A_num, A_int, strT0: "A<num>", strT1: "A<int>");
   }
 
-  test_interfaceType_covariant_02() {
-    var T = typeParameter('T', variance: Variance.covariant);
-    var A = class_(name: 'A', typeParameters: [T]);
-
-    var A_num = A.instantiate(
-      typeArguments: [numNone],
-      nullabilitySuffix: NullabilitySuffix.none,
-    );
-
-    isSubtype(A_num, A_num, strT0: "A<num>", strT1: "A<num>");
-  }
-
-  test_interfaceType_contravariant_01() {
+  test_interfaceType_contravariant() {
     var T = typeParameter('T', variance: Variance.contravariant);
     var A = class_(name: 'A', typeParameters: [T]);
 
@@ -2891,19 +2880,8 @@ class SubtypeTest extends _SubtypingTestBase {
     );
 
     isSubtype(A_num, A_int, strT0: "A<num>", strT1: "A<int>");
-    isNotSubtype(A_int, A_num, strT0: "A<int>", strT1: "A<num>");
-  }
-
-  test_interfaceType_contravariant_02() {
-    var T = typeParameter('T', variance: Variance.contravariant);
-    var A = class_(name: 'A', typeParameters: [T]);
-
-    var A_num = A.instantiate(
-      typeArguments: [numNone],
-      nullabilitySuffix: NullabilitySuffix.none,
-    );
-
     isSubtype(A_num, A_num, strT0: "A<num>", strT1: "A<num>");
+    isNotSubtype(A_int, A_num, strT0: "A<int>", strT1: "A<num>");
   }
 
   test_interfaceType_invariant() {