diff --git a/prism/src/parser/ast/ASTElement.java b/prism/src/parser/ast/ASTElement.java
index becbc733..4f59bc7b 100644
--- a/prism/src/parser/ast/ASTElement.java
+++ b/prism/src/parser/ast/ASTElement.java
@@ -111,7 +111,7 @@ public abstract class ASTElement
 	/**
 	 * Get the type for this element. It should have already been computed
 	 * by calling typeCheck(). If not, it will be computed first but, in
-	 * the case of error, you will get "unknown" type, not the error.
+	 * the case of error, you will get "unknown" (null) type, not the error.
 	 */
 	public Type getType()
 	{
@@ -128,11 +128,12 @@ public abstract class ASTElement
 	}
 
 	/**
-	 * Get the type for this element, as a string.
+	 * Get the type for this element but, unlike getType(), don't call typeCheck()
+	 * if it has not been computed yet - just return null instead.
 	 */
-	public String getTypeString()
+	public Type getTypeIfDefined()
 	{
-		return type.getTypeString();
+		return type;
 	}
 
 	public boolean hasPosition()
diff --git a/prism/src/parser/visitor/ExpandFormulas.java b/prism/src/parser/visitor/ExpandFormulas.java
index 3ecff782..d7a6caa0 100644
--- a/prism/src/parser/visitor/ExpandFormulas.java
+++ b/prism/src/parser/visitor/ExpandFormulas.java
@@ -67,7 +67,7 @@ public class ExpandFormulas extends ASTTraverseModify
 			expr = Expression.Parenth(expr);
 			// This is probably being done before type-checking so
 			// don't really need to preserve type, but do so just in case
-			t = expr.getType();
+			t = expr.getTypeIfDefined();
 			expr = Expression.Parenth(expr);
 			expr.setType(t);
 			// Return replacement expression