diff --git a/src/language/__tests__/schema-parser-test.js b/src/language/__tests__/schema-parser-test.js
index a9577d12daf..d05a7446100 100644
--- a/src/language/__tests__/schema-parser-test.js
+++ b/src/language/__tests__/schema-parser-test.js
@@ -90,7 +90,10 @@ describe('Schema Parser', () => {
             fieldNode(
               nameNode('world', { start: 15, end: 20 }),
               typeNode('String', { start: 22, end: 28 }),
-              { start: 15, end: 28 },
+              {
+                start: 15,
+                end: 28,
+              },
             ),
           ],
           loc: { start: 0, end: 30 },
@@ -186,7 +189,10 @@ describe('Schema Parser', () => {
             fieldNode(
               nameNode('world', { start: 22, end: 27 }),
               typeNode('String', { start: 29, end: 35 }),
-              { start: 22, end: 35 },
+              {
+                start: 22,
+                end: 35,
+              },
             ),
           ],
           loc: { start: 0, end: 37 },
@@ -333,7 +339,8 @@ describe('Schema Parser', () => {
         world: String
       }
     `).to.deep.equal({
-      message: 'Syntax Error: Unexpected Name "extend".',
+      message:
+        'Syntax Error: Unexpected Name "extend". Extension do not include descriptions.',
       locations: [{ line: 3, column: 7 }],
     });
 
@@ -354,7 +361,8 @@ describe('Schema Parser', () => {
         world: String
       }
     `).to.deep.equal({
-      message: 'Syntax Error: Unexpected Name "extend".',
+      message:
+        'Syntax Error: Unexpected Name "extend". Extension do not include descriptions.',
       locations: [{ line: 3, column: 7 }],
     });
 
@@ -482,7 +490,10 @@ describe('Schema Parser', () => {
             fieldNode(
               nameNode('field', { start: 35, end: 40 }),
               typeNode('String', { start: 42, end: 48 }),
-              { start: 35, end: 48 },
+              {
+                start: 35,
+                end: 48,
+              },
             ),
           ],
           loc: { start: 0, end: 50 },
@@ -508,7 +519,10 @@ describe('Schema Parser', () => {
             fieldNode(
               nameNode('field', { start: 30, end: 35 }),
               typeNode('String', { start: 37, end: 43 }),
-              { start: 30, end: 43 },
+              {
+                start: 30,
+                end: 43,
+              },
             ),
           ],
           loc: { start: 0, end: 45 },
@@ -537,7 +551,10 @@ describe('Schema Parser', () => {
             fieldNode(
               nameNode('field', { start: 33, end: 38 }),
               typeNode('String', { start: 40, end: 46 }),
-              { start: 33, end: 46 },
+              {
+                start: 33,
+                end: 46,
+              },
             ),
           ],
           loc: { start: 0, end: 48 },
@@ -565,7 +582,10 @@ describe('Schema Parser', () => {
             fieldNode(
               nameNode('field', { start: 38, end: 43 }),
               typeNode('String', { start: 45, end: 51 }),
-              { start: 38, end: 51 },
+              {
+                start: 38,
+                end: 51,
+              },
             ),
           ],
           loc: { start: 0, end: 53 },
@@ -594,7 +614,10 @@ describe('Schema Parser', () => {
             fieldNode(
               nameNode('field', { start: 35, end: 40 }),
               typeNode('String', { start: 42, end: 48 }),
-              { start: 35, end: 48 },
+              {
+                start: 35,
+                end: 48,
+              },
             ),
           ],
           loc: { start: 0, end: 50 },
@@ -624,7 +647,10 @@ describe('Schema Parser', () => {
             fieldNode(
               nameNode('field', { start: 40, end: 45 }),
               typeNode('String', { start: 47, end: 53 }),
-              { start: 40, end: 53 },
+              {
+                start: 40,
+                end: 53,
+              },
             ),
           ],
           loc: { start: 0, end: 55 },
@@ -695,7 +721,10 @@ describe('Schema Parser', () => {
             fieldNode(
               nameNode('world', { start: 20, end: 25 }),
               typeNode('String', { start: 27, end: 33 }),
-              { start: 20, end: 33 },
+              {
+                start: 20,
+                end: 33,
+              },
             ),
           ],
           loc: { start: 0, end: 35 },
diff --git a/src/language/parser.js b/src/language/parser.js
index 2fdcdc6ab64..1cb9ff0fafb 100644
--- a/src/language/parser.js
+++ b/src/language/parser.js
@@ -725,7 +725,8 @@ class Parser {
    */
   parseTypeSystemDefinition(): TypeSystemDefinitionNode {
     // Many definitions begin with a description and require a lookahead.
-    const keywordToken = this.peekDescription()
+    const hasDescription = this.peekDescription();
+    const keywordToken = hasDescription
       ? this._lexer.lookahead()
       : this._lexer.token;
 
@@ -750,6 +751,14 @@ class Parser {
       }
     }
 
+    if (hasDescription && keywordToken.value === 'extend') {
+      throw syntaxError(
+        this._lexer.source,
+        keywordToken.start,
+        'Unexpected Name "extend". Extension do not include descriptions.',
+      );
+    }
+
     throw this.unexpected(keywordToken);
   }