diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index 57cb59783f145c..ebae392808bb01 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -2392,6 +2392,9 @@ func conv(n *Node, t *types.Type) *Node {
 // convnop converts node n to type t using the OCONVNOP op
 // and typechecks the result with ctxExpr.
 func convnop(n *Node, t *types.Type) *Node {
+	if types.Identical(n.Type, t) {
+		return n
+	}
 	n = nod(OCONVNOP, n, nil)
 	n.Type = t
 	n = typecheck(n, ctxExpr)
@@ -3915,7 +3918,7 @@ func walkCheckPtrAlignment(n *Node, init *Nodes) *Node {
 	}
 
 	n.Left = cheapexpr(n.Left, init)
-	init.Append(mkcall("checkptrAlignment", nil, init, n.Left, typename(n.Type.Elem())))
+	init.Append(mkcall("checkptrAlignment", nil, init, convnop(n.Left, types.Types[TUNSAFEPTR]), typename(n.Type.Elem())))
 	return n
 }
 
@@ -3956,7 +3959,7 @@ func walkCheckPtrArithmetic(n *Node, init *Nodes) *Node {
 		case OCONVNOP:
 			if n.Left.Type.Etype == TUNSAFEPTR {
 				n.Left = cheapexpr(n.Left, init)
-				originals = append(originals, n.Left)
+				originals = append(originals, convnop(n.Left, types.Types[TUNSAFEPTR]))
 			}
 		}
 	}
@@ -3968,7 +3971,7 @@ func walkCheckPtrArithmetic(n *Node, init *Nodes) *Node {
 	slice.Esc = EscNone
 	slice.SetTransient(true)
 
-	init.Append(mkcall("checkptrArithmetic", nil, init, n, slice))
+	init.Append(mkcall("checkptrArithmetic", nil, init, convnop(n, types.Types[TUNSAFEPTR]), slice))
 	return n
 }
 
diff --git a/test/fixedbugs/issue34966.go b/test/fixedbugs/issue34966.go
new file mode 100644
index 00000000000000..f920e71a6d7965
--- /dev/null
+++ b/test/fixedbugs/issue34966.go
@@ -0,0 +1,14 @@
+// compile -d=checkptr
+
+// Copyright 2019 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 p
+
+import "unsafe"
+
+type ptr unsafe.Pointer
+
+func f(p ptr) *int { return (*int)(p) }
+func g(p ptr) ptr  { return ptr(uintptr(p) + 1) }