diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go
index 121dfb75e5..92eae0a458 100644
--- a/src/cmd/compile/internal/syntax/parser.go
+++ b/src/cmd/compile/internal/syntax/parser.go
@@ -1680,7 +1680,12 @@ func (p *parser) header(forStmt bool) (init SimpleStmt, cond Expr, post SimpleSt
 	case *ExprStmt:
 		cond = s.X
 	default:
-		p.error("invalid condition, tag, or type switch guard")
+		// Not obviously a syntax error but by making it one, we get
+		// automatic filtering of multiple syntax error messages per
+		// line in the compiler. This avoids the follow-up error
+		// "missing condition in if statement" for an if statement
+		// (minimal fix for #18915).
+		p.syntax_error(fmt.Sprintf("%s used as value", String(s)))
 	}
 
 	p.xnest = outer
diff --git a/test/fixedbugs/issue18915.go b/test/fixedbugs/issue18915.go
new file mode 100644
index 0000000000..a432bbc17c
--- /dev/null
+++ b/test/fixedbugs/issue18915.go
@@ -0,0 +1,21 @@
+// errorcheck
+
+// Copyright 2017 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.
+
+// Make sure error message for invalid conditions
+// or tags are consistent with earlier Go versions.
+
+package p
+
+func _() {
+	if a := 10 { // ERROR "a := 10 used as value"
+	}
+
+	for b := 10 { // ERROR "b := 10 used as value"
+	}
+
+	switch c := 10 { // ERROR "c := 10 used as value"
+	}
+}