diff --git a/algebricks/algebricks-rewriter/src/main/java/edu/uci/ics/hyracks/algebricks/rewriter/rules/ExtractCommonExpressionsRule.java b/algebricks/algebricks-rewriter/src/main/java/edu/uci/ics/hyracks/algebricks/rewriter/rules/ExtractCommonExpressionsRule.java
index 9e0d8d0..eafb3b0 100644
--- a/algebricks/algebricks-rewriter/src/main/java/edu/uci/ics/hyracks/algebricks/rewriter/rules/ExtractCommonExpressionsRule.java
+++ b/algebricks/algebricks-rewriter/src/main/java/edu/uci/ics/hyracks/algebricks/rewriter/rules/ExtractCommonExpressionsRule.java
@@ -251,7 +251,7 @@
                         return true;
                     }
                 } else {
-                    if (assignCommonExpression(exprEqClass, expr)) {
+                    if (expr.isFunctional() && assignCommonExpression(exprEqClass, expr)) {
                         //re-obtain the live vars after rewriting in the method called in the if condition
                         Set<LogicalVariable> liveVars = new HashSet<LogicalVariable>();
                         VariableUtilities.getLiveVariables(op, liveVars);