diff --git a/ee.h b/ee.h
index cbb6d5c..10d30f7 100644
--- a/ee.h
+++ b/ee.h
@@ -107,9 +107,11 @@ evaluate(STACK* target_stack, int operator){
             break;
         case '!' :
             operands = getOperands(target_stack, 1);
-            if ((operands[0] != floor(operands[0])))
+            if ( (operands[0] != floor(operands[0])) || (operands[0] < 0))
                 { ERR_INVALID_FACTORIAL = 1; }
-            value = fact((int)operands[0]);
+            else{
+                value = fact((int)operands[0]);
+            }
             break;
         default :
             break;
@@ -151,14 +153,14 @@ reportErrors(){
      * ERR_INVALID_INPUT.
      */
     int errors = 0;
-    if (ERR_NS_OPERANDS){
-        printf("Error: insufficient operands.\n"); errors++;
+    if (ERR_INVALID_INPUT){
+        printf("Error: Unexpected input.\n"); errors++;
     } else if (ERR_NS_OPERATORS){
         printf("Error: insufficient operators.\n"); errors++;
-    } else if (ERR_INVALID_INPUT){
-        printf("Error: Unexpected input.\n"); errors++;
+    } else if (ERR_NS_OPERANDS){
+        printf("Error: insufficient operands.\n"); errors++;
     } else if (ERR_INVALID_FACTORIAL){
-        printf("Error: only integer factorials are supported.\n"); errors++;
+        printf("Error: Factorials are only supported for positive integers.\n"); errors++;
     }
     return errors;
 }