1 files changed, 3 insertions, 1 deletions
diff --git a/compiler/semstmts.nim b/compiler/semstmts.nim
index edce7c9bd..15bfaab10 100644
--- a/compiler/semstmts.nim
+++ b/compiler/semstmts.nim
@@ -944,13 +944,15 @@ proc semLambda(c: PContext, n: PNode, flags: TExprFlags): PNode =
       localError(n.sons[bodyPos].info, errImplOfXNotAllowed, s.name.s)
     #if efDetermineType notin flags:
     # XXX not good enough; see tnamedparamanonproc.nim
-    if n.sons[genericParamsPos].kind == nkEmpty:
+    if gp.len == 0 or (gp.len == 1 and tfRetType in gp[0].typ.flags):
       pushProcCon(c, s)
       addResult(c, s.typ.sons[0], n.info, skProc)
       let semBody = hloBody(c, semProcBody(c, n.sons[bodyPos]))
       n.sons[bodyPos] = transformBody(c.module, semBody, s)
       addResultNode(c, n)
       popProcCon(c)
+    elif efOperand notin flags:
+      localError(n.info, errGenericLambdaNotAllowed)
     sideEffectsCheck(c, s)
   else:
     localError(n.info, errImplOfXexpected, s.name.s)