diff --git a/.changeset/thin-berries-deny.md b/.changeset/thin-berries-deny.md
new file mode 100644
index 00000000000..02522f7b719
--- /dev/null
+++ b/.changeset/thin-berries-deny.md
@@ -0,0 +1,5 @@
+---
+'@graphql-codegen/visitor-plugin-common': patch
+---
+
+Output valid type names with mergeFragmentTypes
diff --git a/packages/plugins/other/visitor-plugin-common/src/selection-set-to-object.ts b/packages/plugins/other/visitor-plugin-common/src/selection-set-to-object.ts
index 3ec5bd632ec..f25a876ce9a 100644
--- a/packages/plugins/other/visitor-plugin-common/src/selection-set-to-object.ts
+++ b/packages/plugins/other/visitor-plugin-common/src/selection-set-to-object.ts
@@ -459,10 +459,13 @@ export class SelectionSetToObject<Config extends ParsedDocumentsConfig = ParsedD
         // then don't have a typename for naming the fragment.
         acc[
           selectedTypes.length <= 3
-            ? selectedTypes.join('_')
+            ? // Remove quote marks to produce a valid type name
+              selectedTypes.map(t => t.replace(/'/g, '')).join('_')
             : createHash('sha256')
                 .update(selectedTypes.join() || transformedSet || '')
+                // Remove invalid characters to produce a valid type name
                 .digest('base64')
+                .replace(/[=+/]/g, '')
         ] = [transformedSet];
       }
       return acc;
diff --git a/packages/plugins/typescript/operations/tests/ts-documents.spec.ts b/packages/plugins/typescript/operations/tests/ts-documents.spec.ts
index 7447163c474..60b37b0e625 100644
--- a/packages/plugins/typescript/operations/tests/ts-documents.spec.ts
+++ b/packages/plugins/typescript/operations/tests/ts-documents.spec.ts
@@ -2227,15 +2227,15 @@ describe('TypeScript Operations Plugin', () => {
           id
         }
       `);
-      const config = { preResolveTypes: true, mergeFragmentTypes: true };
+      const config = { preResolveTypes: true, mergeFragmentTypes: true, namingConvention: 'keep' };
       const { content } = await plugin(schema, [{ location: 'test-file.ts', document: ast }], config, {
         outputFile: '',
       });
 
       expect(content).toBeSimilarStringTo(`
-        export type TestQueryVariables = Exact<{ [key: string]: never; }>;
+        export type testQueryVariables = Exact<{ [key: string]: never; }>;
 
-        export type TestQuery = (
+        export type testQuery = (
           { notifications: Array<(
             { id: string }
             & { __typename?: 'TextNotification' | 'ImageNotification' }
@@ -2260,7 +2260,7 @@ describe('TypeScript Operations Plugin', () => {
           }
         }
       `);
-      const config = { preResolveTypes: true, mergeFragmentTypes: true };
+      const config = { preResolveTypes: true, mergeFragmentTypes: true, namingConvention: 'keep' };
       const { content } = await plugin(schema, [{ location: 'test-file.ts', document: ast }], config, {
         outputFile: '',
       });
@@ -2321,7 +2321,7 @@ describe('TypeScript Operations Plugin', () => {
           }
         }
       `);
-      const config = { preResolveTypes: true, mergeFragmentTypes: true };
+      const config = { preResolveTypes: true, mergeFragmentTypes: true, namingConvention: 'keep' };
       const { content } = await plugin(testSchema, [{ location: 'test-file.ts', document: ast }], config, {
         outputFile: '',
       });
@@ -2332,12 +2332,12 @@ describe('TypeScript Operations Plugin', () => {
            & { __typename?: 'A' }
          );
 
-         type N_ZhJjUzpMTyh98zugnx0IKwiLetPNjV8KYbSlmpAeuu_Fragment = (
+         type N_zhJJUzpMTyh98zugnx0IKwiLetPNjV8KybSlmpAEUU_Fragment = (
            { id: string }
            & { __typename?: 'B' | 'C' | 'D' | 'E' }
          );
 
-         export type NFragment = N_A_Fragment | N_ZhJjUzpMTyh98zugnx0IKwiLetPNjV8KYbSlmpAeuu_Fragment;
+         export type NFragment = N_A_Fragment | N_zhJJUzpMTyh98zugnx0IKwiLetPNjV8KybSlmpAEUU_Fragment;
       `);
       await validate(content, config);
     });
@@ -2352,7 +2352,7 @@ describe('TypeScript Operations Plugin', () => {
           }
         }
       `);
-      const config = { preResolveTypes: true, mergeFragmentTypes: true };
+      const config = { preResolveTypes: true, mergeFragmentTypes: true, namingConvention: 'keep' };
       const { content } = await plugin(schema, [{ location: 'test-file.ts', document: ast }], config, {
         outputFile: '',
       });
@@ -2381,15 +2381,15 @@ describe('TypeScript Operations Plugin', () => {
           id
         }
       `);
-      const config = { preResolveTypes: true, skipTypename: true, mergeFragmentTypes: true };
+      const config = { preResolveTypes: true, skipTypename: true, mergeFragmentTypes: true, namingConvention: 'keep' };
       const { content } = await plugin(schema, [{ location: 'test-file.ts', document: ast }], config, {
         outputFile: '',
       });
 
       expect(content).toBeSimilarStringTo(`
-        export type TestQueryVariables = Exact<{ [key: string]: never; }>;
+        export type testQueryVariables = Exact<{ [key: string]: never; }>;
 
-        export type TestQuery = { notifications: Array<{ id: string }> };
+        export type testQuery = { notifications: Array<{ id: string }> };
       `);
       await validate(content, config);
     });
@@ -2403,7 +2403,7 @@ describe('TypeScript Operations Plugin', () => {
           }
         }
       `);
-      const config = { preResolveTypes: true, skipTypename: true, mergeFragmentTypes: true };
+      const config = { preResolveTypes: true, skipTypename: true, mergeFragmentTypes: true, namingConvention: 'keep' };
       const { content } = await plugin(schema, [{ location: 'test-file.ts', document: ast }], config, {
         outputFile: '',
       });