diff --git a/modules/libcom/src/calc/postfix.c b/modules/libcom/src/calc/postfix.c
index 8007d1e1d..c510917d1 100644
--- a/modules/libcom/src/calc/postfix.c
+++ b/modules/libcom/src/calc/postfix.c
@@ -336,6 +336,10 @@ LIBCOM_API long
             break;
 
         case SEPERATOR:
+            if (pstacktop == stack) {
+                *perror = CALC_ERR_BAD_SEPERATOR;
+                goto bad;
+            }
             /* Move operators to the output until open paren */
             while (pstacktop->name[0] != '(') {
                 if (pstacktop <= stack+1) {
@@ -354,6 +358,10 @@ LIBCOM_API long
             break;
 
         case CLOSE_PAREN:
+            if (pstacktop == stack) {
+                *perror = CALC_ERR_PAREN_NOT_OPEN;
+                goto bad;
+            }
             /* Move operators to the output until matching paren */
             while (pstacktop->name[0] != '(') {
                 if (pstacktop <= stack+1) {
diff --git a/modules/libcom/test/epicsCalcTest.cpp b/modules/libcom/test/epicsCalcTest.cpp
index 9734caf3c..c794fa1cb 100644
--- a/modules/libcom/test/epicsCalcTest.cpp
+++ b/modules/libcom/test/epicsCalcTest.cpp
@@ -298,7 +298,7 @@ MAIN(epicsCalcTest)
     const double a=1.0, b=2.0, c=3.0, d=4.0, e=5.0, f=6.0,
                  g=7.0, h=8.0, i=9.0, j=10.0, k=11.0, l=12.0;
 
-    testPlan(/*635*/633);
+    testPlan(637-2);
 
     /* LITERAL_OPERAND elements */
     testExpr(0);
@@ -953,6 +953,8 @@ MAIN(epicsCalcTest)
 //    testBadExpr("1?", CALC_ERR_CONDITIONAL);
 //    testBadExpr("1?1", CALC_ERR_CONDITIONAL);
     testBadExpr(":1", CALC_ERR_SYNTAX);
+    testBadExpr("0,", CALC_ERR_BAD_SEPERATOR);
+    testBadExpr("0)", CALC_ERR_PAREN_NOT_OPEN);
 
     // Bit manipulations wrt bit 31 (bug lp:1514520)
     //   using integer literals