diff --git a/packages/core/src/helpers/getMarkType.ts b/packages/core/src/helpers/getMarkType.ts
index c65100b2..48bf08a2 100644
--- a/packages/core/src/helpers/getMarkType.ts
+++ b/packages/core/src/helpers/getMarkType.ts
@@ -2,6 +2,10 @@ import { MarkType, Schema } from 'prosemirror-model'
 
 export default function getMarkType(nameOrType: string | MarkType, schema: Schema): MarkType {
   if (typeof nameOrType === 'string') {
+    if (!schema.marks[nameOrType]) {
+      throw Error(`There is no mark type named '${nameOrType}'. Maybe you forgot to add the extension?`)
+    }
+
     return schema.marks[nameOrType]
   }
 
diff --git a/packages/core/src/helpers/getNodeType.ts b/packages/core/src/helpers/getNodeType.ts
index 58da4f70..27430105 100644
--- a/packages/core/src/helpers/getNodeType.ts
+++ b/packages/core/src/helpers/getNodeType.ts
@@ -2,6 +2,10 @@ import { NodeType, Schema } from 'prosemirror-model'
 
 export default function getNodeType(nameOrType: string | NodeType, schema: Schema): NodeType {
   if (typeof nameOrType === 'string') {
+    if (!schema.nodes[nameOrType]) {
+      throw Error(`There is no node type named '${nameOrType}'. Maybe you forgot to add the extension?`)
+    }
+
     return schema.nodes[nameOrType]
   }