diff --git a/.eslintrc.yml b/.eslintrc.yml
index e18d27e027..50fd1f85f9 100644
--- a/.eslintrc.yml
+++ b/.eslintrc.yml
@@ -538,7 +538,7 @@ overrides:
       '@typescript-eslint/restrict-template-expressions': off #TODO temporarily disabled
       '@typescript-eslint/sort-type-union-intersection-members': off # TODO consider
       '@typescript-eslint/strict-boolean-expressions': off # TODO consider
-      '@typescript-eslint/switch-exhaustiveness-check': off #TODO temporarily disabled
+      '@typescript-eslint/switch-exhaustiveness-check': error
       '@typescript-eslint/triple-slash-reference': error
       '@typescript-eslint/typedef': off
       '@typescript-eslint/unbound-method': off # TODO consider
diff --git a/src/__tests__/starWarsSchema.ts b/src/__tests__/starWarsSchema.ts
index 2cc586a6ac..7bd8fb3e8f 100644
--- a/src/__tests__/starWarsSchema.ts
+++ b/src/__tests__/starWarsSchema.ts
@@ -1,5 +1,3 @@
-import { invariant } from '../jsutils/invariant';
-
 import { GraphQLSchema } from '../type/schema';
 import { GraphQLString } from '../type/scalars';
 import {
@@ -137,9 +135,6 @@ const characterInterface: GraphQLInterfaceType = new GraphQLInterfaceType({
       case 'Droid':
         return droidType.name;
     }
-
-    // istanbul ignore next (Not reachable. All possible types have been considered)
-    invariant(false);
   },
 });
 
diff --git a/src/execution/execute.ts b/src/execution/execute.ts
index 3dbb6c5cdd..cab22dfd13 100644
--- a/src/execution/execute.ts
+++ b/src/execution/execute.ts
@@ -309,6 +309,8 @@ export function buildExecutionContext(
       case Kind.FRAGMENT_DEFINITION:
         fragments[definition.name.value] = definition;
         break;
+      default:
+      // ignore non-executable definitions
     }
   }
 
diff --git a/src/language/parser.ts b/src/language/parser.ts
index 1b0bc75f92..4c1725cce4 100644
--- a/src/language/parser.ts
+++ b/src/language/parser.ts
@@ -619,8 +619,9 @@ export class Parser {
           }
         }
         return this.parseVariable();
+      default:
+        throw this.unexpected();
     }
-    throw this.unexpected();
   }
 
   parseConstValueLiteral(): ConstValueNode {
diff --git a/src/type/schema.ts b/src/type/schema.ts
index d8a749dfd4..1842857905 100644
--- a/src/type/schema.ts
+++ b/src/type/schema.ts
@@ -9,10 +9,10 @@ import type { Maybe } from '../jsutils/Maybe';
 import type { GraphQLError } from '../error/GraphQLError';
 
 import type {
-  OperationTypeNode,
   SchemaDefinitionNode,
   SchemaExtensionNode,
 } from '../language/ast';
+import { OperationTypeNode } from '../language/ast';
 
 import type {
   GraphQLType,
@@ -282,11 +282,11 @@ export class GraphQLSchema {
 
   getRootType(operation: OperationTypeNode): Maybe<GraphQLObjectType> {
     switch (operation) {
-      case 'query':
+      case OperationTypeNode.QUERY:
         return this.getQueryType();
-      case 'mutation':
+      case OperationTypeNode.MUTATION:
         return this.getMutationType();
-      case 'subscription':
+      case OperationTypeNode.SUBSCRIPTION:
         return this.getSubscriptionType();
     }
   }
diff --git a/src/utilities/TypeInfo.ts b/src/utilities/TypeInfo.ts
index a737db8c39..7b316b963f 100644
--- a/src/utilities/TypeInfo.ts
+++ b/src/utilities/TypeInfo.ts
@@ -247,6 +247,8 @@ export class TypeInfo {
         this._enumValue = enumValue;
         break;
       }
+      default:
+      // Ignore other nodes
     }
   }
 
@@ -283,6 +285,8 @@ export class TypeInfo {
       case Kind.ENUM:
         this._enumValue = null;
         break;
+      default:
+      // Ignore other nodes
     }
   }
 }
diff --git a/src/utilities/__tests__/separateOperations-test.ts b/src/utilities/__tests__/separateOperations-test.ts
index 3ebe1a5f57..2f14bae9ac 100644
--- a/src/utilities/__tests__/separateOperations-test.ts
+++ b/src/utilities/__tests__/separateOperations-test.ts
@@ -201,6 +201,34 @@ describe('separateOperations', () => {
     });
   });
 
+  it('ignores type definitions', () => {
+    const ast = parse(`
+      query Foo {
+        ...Bar
+      }
+
+      fragment Bar on T {
+        baz
+      }
+
+      scalar Foo
+      type Bar
+    `);
+
+    const separatedASTs = mapValue(separateOperations(ast), print);
+    expect(separatedASTs).to.deep.equal({
+      Foo: dedent`
+        query Foo {
+          ...Bar
+        }
+
+        fragment Bar on T {
+          baz
+        }
+      `,
+    });
+  });
+
   it('handles unknown fragments', () => {
     const ast = parse(`
       {
diff --git a/src/utilities/buildClientSchema.ts b/src/utilities/buildClientSchema.ts
index e2d55eecb1..138f7f2625 100644
--- a/src/utilities/buildClientSchema.ts
+++ b/src/utilities/buildClientSchema.ts
@@ -173,6 +173,8 @@ export function buildClientSchema(
   function buildType(type: IntrospectionType): GraphQLNamedType {
     // eslint-disable-next-line @typescript-eslint/prefer-optional-chain
     if (type != null && type.name != null && type.kind != null) {
+      // FIXME: Properly type IntrospectionType, it's a breaking change so fix in v17
+      // eslint-disable-next-line @typescript-eslint/switch-exhaustiveness-check
       switch (type.kind) {
         case TypeKind.SCALAR:
           return buildScalarDef(type);
diff --git a/src/utilities/extendSchema.ts b/src/utilities/extendSchema.ts
index 6a96ddb3f5..c952a4b40e 100644
--- a/src/utilities/extendSchema.ts
+++ b/src/utilities/extendSchema.ts
@@ -649,9 +649,6 @@ export function extendSchemaImpl(
         });
       }
     }
-
-    // istanbul ignore next (Not reachable. All possible type definition nodes have been considered)
-    invariant(false, 'Unexpected type definition node: ' + inspect(astNode));
   }
 }
 
diff --git a/src/utilities/separateOperations.ts b/src/utilities/separateOperations.ts
index ece8c2739d..84a8b774f9 100644
--- a/src/utilities/separateOperations.ts
+++ b/src/utilities/separateOperations.ts
@@ -31,6 +31,8 @@ export function separateOperations(
           definitionNode.selectionSet,
         );
         break;
+      default:
+      // ignore non-executable definitions
     }
   }
 
diff --git a/src/utilities/valueFromASTUntyped.ts b/src/utilities/valueFromASTUntyped.ts
index c3e2e92e49..678ea15128 100644
--- a/src/utilities/valueFromASTUntyped.ts
+++ b/src/utilities/valueFromASTUntyped.ts
@@ -1,6 +1,4 @@
 import type { ObjMap } from '../jsutils/ObjMap';
-import { inspect } from '../jsutils/inspect';
-import { invariant } from '../jsutils/invariant';
 import { keyValMap } from '../jsutils/keyValMap';
 import type { Maybe } from '../jsutils/Maybe';
 
@@ -51,7 +49,4 @@ export function valueFromASTUntyped(
     case Kind.VARIABLE:
       return variables?.[valueNode.name.value];
   }
-
-  // istanbul ignore next (Not reachable. All possible value nodes have been considered)
-  invariant(false, 'Unexpected value node: ' + inspect(valueNode));
 }
diff --git a/src/validation/rules/KnownDirectivesRule.ts b/src/validation/rules/KnownDirectivesRule.ts
index 53c98db3a8..20cf7fa024 100644
--- a/src/validation/rules/KnownDirectivesRule.ts
+++ b/src/validation/rules/KnownDirectivesRule.ts
@@ -120,6 +120,9 @@ function getDirectiveLocationForASTPath(
         ? DirectiveLocation.INPUT_FIELD_DEFINITION
         : DirectiveLocation.ARGUMENT_DEFINITION;
     }
+    // istanbul ignore next (Not reachable. All possible types have been considered)
+    default:
+      invariant(false, 'Unexpected kind: ' + inspect(appliedTo.kind));
   }
 }
 
@@ -134,7 +137,4 @@ function getDirectiveLocationForOperation(
     case OperationTypeNode.SUBSCRIPTION:
       return DirectiveLocation.SUBSCRIPTION;
   }
-
-  // istanbul ignore next (Not reachable. All possible types have been considered)
-  invariant(false, 'Unexpected operation: ' + inspect(operation));
 }
diff --git a/src/validation/rules/PossibleTypeExtensionsRule.ts b/src/validation/rules/PossibleTypeExtensionsRule.ts
index 27016fffd8..fe014fe7d6 100644
--- a/src/validation/rules/PossibleTypeExtensionsRule.ts
+++ b/src/validation/rules/PossibleTypeExtensionsRule.ts
@@ -137,8 +137,8 @@ function extensionKindToTypeName(kind: Kind): string {
       return 'enum';
     case Kind.INPUT_OBJECT_TYPE_EXTENSION:
       return 'input object';
+    // istanbul ignore next (Not reachable. All possible types have been considered)
+    default:
+      invariant(false, 'Unexpected kind: ' + inspect(kind));
   }
-
-  // istanbul ignore next (Not reachable. All possible types have been considered)
-  invariant(false, 'Unexpected kind: ' + inspect(kind));
 }