diff --git a/common/fko_util.c b/common/fko_util.c
index 07aa18ed..4b293163 100644
--- a/common/fko_util.c
+++ b/common/fko_util.c
@@ -1142,11 +1142,9 @@ count_characters(const char *str, const char match, int len)
 {
     int i, count = 0;
 
-    for (i=0; i < len; i++) {
+    for (i=0; i < len && str[i] != '\0'; i++) {
         if (str[i] == match)
             count++;
-        if (str[i] == '\0')
-            return count;
     }
     return count;
 }
diff --git a/test/tests/basic_operations.pl b/test/tests/basic_operations.pl
index a50a1baf..3b909d55 100644
--- a/test/tests/basic_operations.pl
+++ b/test/tests/basic_operations.pl
@@ -192,6 +192,27 @@
         'exec_err' => $YES,
         'cmdline' => "$fwknopCmd -A tcp/600001 -a $fake_ip -D $loopback_ip",
     },
+
+    ### trigger strtol() error
+    {
+        'category' => 'basic operations',
+        'subcategory' => 'client',
+        'detail'   => 'invalid SPA destination port (1)',
+        'function' => \&generic_exec,
+        'exec_err' => $YES,
+        'cmdline' => "$fwknopCmd -A tcp/22 -a $fake_ip -D $loopback_ip -p 9999999999999999999999999999999999999999999999999999999999",
+    },
+
+    ### trigger MAX_PORT error
+    {
+        'category' => 'basic operations',
+        'subcategory' => 'client',
+        'detail'   => 'invalid SPA destination port (2)',
+        'function' => \&generic_exec,
+        'exec_err' => $YES,
+        'cmdline' => "$fwknopCmd -A tcp/22 -a $fake_ip -D $loopback_ip -p 99999",
+    },
+
     {
         'category' => 'basic operations',
         'subcategory' => 'client',