diff --git a/src/cmd/compile/internal/gc/closure.go b/src/cmd/compile/internal/gc/closure.go
index 04fb7d5..23e48939 100644
--- a/src/cmd/compile/internal/gc/closure.go
+++ b/src/cmd/compile/internal/gc/closure.go
@@ -108,7 +108,17 @@
 
 	xfunc.Func.Nname.Sym = closurename(Curfn)
 	disableExport(xfunc.Func.Nname.Sym)
-	declare(xfunc.Func.Nname, PFUNC)
+	if xfunc.Func.Nname.Sym.Def != nil {
+		// The only case we can reach here is when the outer function was redeclared.
+		// In that case, don't bother to redeclare the closure. Otherwise, we will get
+		// a spurious error message, see #17758. While we are here, double check that
+		// we already reported other error.
+		if nsavederrors+nerrors == 0 {
+			Fatalf("unexpected symbol collision %v", xfunc.Func.Nname.Sym)
+		}
+	} else {
+		declare(xfunc.Func.Nname, PFUNC)
+	}
 	xfunc = typecheck(xfunc, ctxStmt)
 
 	// Type check the body now, but only if we're inside a function.
diff --git a/test/fixedbugs/issue17758.go b/test/fixedbugs/issue17758.go
new file mode 100644
index 0000000..e7f2f3a
--- /dev/null
+++ b/test/fixedbugs/issue17758.go
@@ -0,0 +1,17 @@
+// errorcheck
+
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+func foo() {
+	_ = func() {}
+}
+
+func foo() { // ERROR "foo redeclared in this block"
+	_ = func() {}
+}
+
+func main() {}