diff --git a/php/src/StateException.php b/php/src/StateException.php
index b54d13a..3eadf1d 100644
--- a/php/src/StateException.php
+++ b/php/src/StateException.php
@@ -15,9 +15,9 @@ class StateException extends LogicException {
     return new static($prefix.$message);
   }
 
-  static final function unexpected_state(?string $prefix=null): self {
+  static final function unexpected_state(?string $suffix=null): self {
     $message = "unexpected state";
-    if ($prefix) $prefix = "$prefix: ";
-    return new static($prefix.$message);
+    if ($suffix) $suffix = ": $suffix";
+    return new static($message.$suffix);
   }
 }