diff --git a/src/cmd/compile/internal/ssa/check.go b/src/cmd/compile/internal/ssa/check.go
index de77aff480..721e451f05 100644
--- a/src/cmd/compile/internal/ssa/check.go
+++ b/src/cmd/compile/internal/ssa/check.go
@@ -102,7 +102,7 @@ func checkFunc(f *Func) {
 				f.Fatalf("plain/dead block %s has a control value", b)
 			}
 		}
-		if len(b.Succs) > 2 && b.Likely != BranchUnknown {
+		if len(b.Succs) != 2 && b.Likely != BranchUnknown {
 			f.Fatalf("likeliness prediction %d for block %s with %d successors", b.Likely, b, len(b.Succs))
 		}
 
diff --git a/src/cmd/compile/internal/ssa/fuse.go b/src/cmd/compile/internal/ssa/fuse.go
index f00356a7b2..45b13a050d 100644
--- a/src/cmd/compile/internal/ssa/fuse.go
+++ b/src/cmd/compile/internal/ssa/fuse.go
@@ -92,6 +92,7 @@ func fuseBlockIf(b *Block) bool {
 		b.removeEdge(1)
 	}
 	b.Kind = BlockPlain
+	b.Likely = BranchUnknown
 	b.SetControl(nil)
 
 	// Trash the empty blocks s0 & s1.
diff --git a/test/fixedbugs/issue23504.go b/test/fixedbugs/issue23504.go
new file mode 100644
index 0000000000..77f3184149
--- /dev/null
+++ b/test/fixedbugs/issue23504.go
@@ -0,0 +1,15 @@
+// compile
+
+// Copyright 2018 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
+
+func f() {
+	var B bool
+	B2 := (B || B && !B) && !B
+	B3 := B2 || B
+	for (B3 || B2) && !B2 && B {
+	}
+}