diff --git a/flink-metrics/flink-metrics-core/src/main/java/org/apache/flink/metrics/MetricConfig.java b/flink-metrics/flink-metrics-core/src/main/java/org/apache/flink/metrics/MetricConfig.java
index b9fcafb5f2d8a..5d2ca6f83a111 100644
--- a/flink-metrics/flink-metrics-core/src/main/java/org/apache/flink/metrics/MetricConfig.java
+++ b/flink-metrics/flink-metrics-core/src/main/java/org/apache/flink/metrics/MetricConfig.java
@@ -34,7 +34,11 @@
 public class MetricConfig extends Properties {
 
     public String getString(String key, String defaultValue) {
-        return getProperty(key, defaultValue);
+        final Object value = get(key);
+        if (value == null) {
+            return defaultValue;
+        }
+        return value.toString();
     }
 
     /**
diff --git a/flink-metrics/flink-metrics-core/src/test/java/org/apache/flink/metrics/MetricConfigTest.java b/flink-metrics/flink-metrics-core/src/test/java/org/apache/flink/metrics/MetricConfigTest.java
index d3be33d966383..2824328c6a5cd 100644
--- a/flink-metrics/flink-metrics-core/src/test/java/org/apache/flink/metrics/MetricConfigTest.java
+++ b/flink-metrics/flink-metrics-core/src/test/java/org/apache/flink/metrics/MetricConfigTest.java
@@ -90,7 +90,14 @@ private static Stream<Arguments> nativeTypeCases() {
                         123456789012345L),
                 Arguments.of(3.14f, (TypedGetter) (c, k) -> c.getFloat(k, 0.0f), 3.14f),
                 Arguments.of(2.718281828, (TypedGetter) (c, k) -> c.getDouble(k, 0.0), 2.718281828),
-                Arguments.of(true, (TypedGetter) (c, k) -> c.getBoolean(k, false), true));
+                Arguments.of(true, (TypedGetter) (c, k) -> c.getBoolean(k, false), true),
+                Arguments.of(42, (TypedGetter) (c, k) -> c.getString(k, "default"), "42"),
+                Arguments.of(
+                        123456789012345L,
+                        (TypedGetter) (c, k) -> c.getString(k, "default"),
+                        "123456789012345"),
+                Arguments.of(3.14f, (TypedGetter) (c, k) -> c.getString(k, "default"), "3.14"),
+                Arguments.of(true, (TypedGetter) (c, k) -> c.getString(k, "default"), "true"));
     }
 
     private static Stream<Arguments> crossTypeCases() {