diff --git a/src/ParameterResolver.php b/src/ParameterResolver.php
index 3a3c86d..cd08789 100644
--- a/src/ParameterResolver.php
+++ b/src/ParameterResolver.php
@@ -114,7 +114,7 @@ protected function replaceSurroundingToken(string $parameter, string $token, cal
     {
         $oldParameter = $parameter;
 
-        while (mb_substr_count($parameter, $token) > 0) {
+        while (is_string($parameter) && mb_substr_count($parameter, $token) > 0) {
             $pos1 = mb_strpos($parameter, $token);
             $pos2 = mb_strpos($parameter, $token, $pos1 + 1);
 
@@ -126,22 +126,25 @@ protected function replaceSurroundingToken(string $parameter, string $token, cal
             if ($pos2 === false) {
                 throw new ConfigException("An uneven number of '{$token}' token bindings exists for '{$oldParameter}'");
             }
+
             $value = mb_substr($parameter, $pos1 + 1, $pos2 - ($pos1 + 1));
             $newValue = $callable($value);
-            if (!is_string($newValue) && !is_numeric($newValue)) {
-                if (mb_strlen($value) + 2 === mb_strlen($parameter)) {
-                    return $newValue;
-                }
 
+            // If it took up the entire parameter
+            if (($pos1 === 0 && ($pos2 + 1) === mb_strlen($parameter))) {
+                $parameter = $newValue;
+                continue;
+            }
+
+            if (!is_string($newValue) && !is_numeric($newValue)) {
                 throw new ConfigException(
                     "Parameter '{$value}' as part of '{$oldParameter}' resolved to a non-string. This is only permissible if the parameter attempts no interpolation"
                 );
             }
-
             $parameter = mb_substr($parameter, 0, $pos1) . $newValue . mb_substr($parameter, $pos2 + 1);
         }
 
-        return str_replace(self::ESCAPED_TOKEN, $token, $parameter);
+        return is_string($parameter) ? str_replace(self::ESCAPED_TOKEN, $token, $parameter) : $parameter;
     }
 
     public function getResolvedConstants() : array
diff --git a/tests/integration/Basic/BasicTest.php b/tests/integration/Basic/BasicTest.php
index b9cdf98..462969f 100644
--- a/tests/integration/Basic/BasicTest.php
+++ b/tests/integration/Basic/BasicTest.php
@@ -24,6 +24,9 @@ public function testBasic()
         $this->assertEquals("MyService1", $container["my_service"]->getFirstArgument());
         $this->assertInstanceOf(ExampleClass::class, $container["my_service_2"]);
         $this->assertEquals("MyService2", $container["my_service_2"]->getFirstArgument());
+        $arguments = $container["my_service_2"]->getArguments();
+
+        self::assertSame("potatosalad", $arguments[3]);
     }
 
     public function testBoolAndInt()
diff --git a/tests/integration/Basic/file1.yml b/tests/integration/Basic/file1.yml
index 9973fd4..3a8a9f7 100644
--- a/tests/integration/Basic/file1.yml
+++ b/tests/integration/Basic/file1.yml
@@ -10,6 +10,7 @@ services:
       - "%my_parameter_2%"
       - "%my_parameter_3%"
       - "%my_parameter_5%"
+      - "%my_parameter_7%%my_parameter_8%"
 
 parameters:
   my_parameter_2: "MyService2"
@@ -19,3 +20,6 @@ parameters:
 
   my_parameter_5: "%my_parameter_6%"
   my_parameter_6: 5003
+
+  my_parameter_7: "potato"
+  my_parameter_8: "salad"
\ No newline at end of file