diff --git a/query/src/org/labkey/query/QueryTestCase.jsp b/query/src/org/labkey/query/QueryTestCase.jsp
index a1e2ff0500d..684f0569dfd 100644
--- a/query/src/org/labkey/query/QueryTestCase.jsp
+++ b/query/src/org/labkey/query/QueryTestCase.jsp
@@ -911,8 +911,10 @@ d,seven,twelve,day,month,date,duration,guid
                 assertFalse(rs.getColumn(1).isHidden());
                 assertEquals("0.00", rs.getColumn(1).getFormat());
             }
-        }
+        },
 
+        // test operators in THEN expression
+        new SqlTest("SELECT CASE WHEN 1=1 THEN 'a' || 'b' ELSE 'x' || 'y' END")
     );
 
     List<SqlTest> postgres = List.of(
diff --git a/query/src/org/labkey/query/sql/SqlBase.g b/query/src/org/labkey/query/sql/SqlBase.g
index 28ad379df35..72c652d9de7 100644
--- a/query/src/org/labkey/query/sql/SqlBase.g
+++ b/query/src/org/labkey/query/sql/SqlBase.g
@@ -729,15 +729,15 @@ caseExpression
 	;
 	
 whenClause
-	: (WHEN^ logicalExpression THEN! unaryExpression)
+	: (WHEN^ logicalExpression THEN! valueExpression)
 	;
 	
 altWhenClause
-	: (WHEN^ unaryExpression THEN! unaryExpression)
+	: (WHEN^ unaryExpression THEN! valueExpression)
 	;
 	
 elseClause
-	: (ELSE^ unaryExpression)
+	: (ELSE^ valueExpression)
 	;