diff --git a/prism/src/parser/visitor/SemanticCheck.java b/prism/src/parser/visitor/SemanticCheck.java
index 8a3d43cf..c1399e7d 100644
--- a/prism/src/parser/visitor/SemanticCheck.java
+++ b/prism/src/parser/visitor/SemanticCheck.java
@@ -441,6 +441,9 @@ public class SemanticCheck extends ASTTraverse
 
 	public void visitPost(ExpressionProb e) throws PrismLangException
 	{
+		if (e.getModifier() != null) {
+			throw new PrismLangException("Modifier \"" + e.getModifier() + "\" not supported for P operator");
+		}
 		if (e.getProb() != null && !e.getProb().isConstant()) {
 			throw new PrismLangException("P operator probability bound is not constant", e.getProb());
 		}
@@ -448,6 +451,9 @@ public class SemanticCheck extends ASTTraverse
 
 	public void visitPost(ExpressionReward e) throws PrismLangException
 	{
+		if (e.getModifier() != null) {
+			throw new PrismLangException("Modifier \"" + e.getModifier() + "\" not supported for P operator");
+		}
 		if (e.getRewardStructIndex() != null) {
 			if (e.getRewardStructIndex() instanceof Expression) {
 				Expression rsi = (Expression) e.getRewardStructIndex();
@@ -481,6 +487,9 @@ public class SemanticCheck extends ASTTraverse
 
 	public void visitPost(ExpressionSS e) throws PrismLangException
 	{
+		if (e.getModifier() != null) {
+			throw new PrismLangException("Modifier \"" + e.getModifier() + "\" not supported for P operator");
+		}
 		if (e.getProb() != null && !e.getProb().isConstant()) {
 			throw new PrismLangException("S operator probability bound is not constant", e.getProb());
 		}