diff --git a/src/acorn/plugins/flow.js b/src/acorn/plugins/flow.js
index fad5277665..189395b6fa 100644
--- a/src/acorn/plugins/flow.js
+++ b/src/acorn/plugins/flow.js
@@ -153,10 +153,15 @@ pp.flow_parseTypeAlias = function (node) {
     node.typeParameters = null
   }
 
+  var oldInType = this.inType;
+  this.inType = true;
+
   this.expect(tt.eq)
 
   node.right = this.flow_parseType()
 
+  this.inType = oldInType;
+
   this.semicolon()
 
   return this.finishNode(node, "TypeAlias")