diff --git a/data-prepper-plugins/prometheus-sink/src/main/java/org/opensearch/dataprepper/plugins/sink/prometheus/service/PrometheusTimeSeries.java b/data-prepper-plugins/prometheus-sink/src/main/java/org/opensearch/dataprepper/plugins/sink/prometheus/service/PrometheusTimeSeries.java
index 423f651056..b42fbe43c6 100644
--- a/data-prepper-plugins/prometheus-sink/src/main/java/org/opensearch/dataprepper/plugins/sink/prometheus/service/PrometheusTimeSeries.java
+++ b/data-prepper-plugins/prometheus-sink/src/main/java/org/opensearch/dataprepper/plugins/sink/prometheus/service/PrometheusTimeSeries.java
@@ -302,11 +302,15 @@ static String sanitizeMetricName(final Metric metric) {
         final boolean isGauge = metric.getKind().equals(Metric.KIND.GAUGE.toString());
         final boolean isCounter = metric.getKind().equals(Metric.KIND.SUM.toString()) &&
                 ((Sum) metric).isMonotonic() &&
-                ((Sum) metric).getAggregationTemporality().equals("AGGREGATION_TEMPORALITY_CUMULATIVE");
+                "AGGREGATION_TEMPORALITY_CUMULATIVE".equals(((Sum) metric).getAggregationTemporality());
 
         StringBuilder metricNameBuilder = new StringBuilder(sanitizeName(name, true, false));
         String suffix = isCounter ? TOTAL_SUFFIX : "";
 
+        if (unit == null) {
+            return metricNameBuilder.append(suffix).toString();
+        }
+
         if (unit.startsWith("{")) {
             return metricNameBuilder.append(suffix).toString();
         }
diff --git a/data-prepper-plugins/prometheus-sink/src/test/java/org/opensearch/dataprepper/plugins/sink/prometheus/service/PrometheusTimeSeriesTest.java b/data-prepper-plugins/prometheus-sink/src/test/java/org/opensearch/dataprepper/plugins/sink/prometheus/service/PrometheusTimeSeriesTest.java
index e6ff20855f..69fc67b6dc 100644
--- a/data-prepper-plugins/prometheus-sink/src/test/java/org/opensearch/dataprepper/plugins/sink/prometheus/service/PrometheusTimeSeriesTest.java
+++ b/data-prepper-plugins/prometheus-sink/src/test/java/org/opensearch/dataprepper/plugins/sink/prometheus/service/PrometheusTimeSeriesTest.java
@@ -12,6 +12,7 @@
 
 import org.apache.commons.lang3.RandomStringUtils;
 
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
@@ -187,6 +188,38 @@ public void testHistogramMetricKey(String unit, String expectedUnitName) throws
         assertTrue(timeSeries.getMetricKey().equals(expectedKey1) || timeSeries.getMetricKey().equals(expectedKey2));
     }
 
+    @Test
+    public void testSumMetricWithNullAggregationTemporality() {
+        final String name = RandomStringUtils.randomAlphabetic(10);
+        Sum sum = createSumMetric(name, "s", true, null);
+        String sanitizedName = PrometheusTimeSeries.sanitizeMetricName(sum);
+        assertThat(sanitizedName, equalTo(name + "_seconds"));
+    }
+
+    @Test
+    public void testGaugeMetricWithNullUnit() {
+        final String name = RandomStringUtils.randomAlphabetic(10);
+        Gauge gauge = createGaugeMetric(name, null);
+        String sanitizedName = PrometheusTimeSeries.sanitizeMetricName(gauge);
+        assertThat(sanitizedName, equalTo(name));
+    }
+
+    @Test
+    public void testSumMetricCounterWithNullUnit() {
+        final String name = RandomStringUtils.randomAlphabetic(10);
+        Sum sum = createSumMetric(name, null, true, "AGGREGATION_TEMPORALITY_CUMULATIVE");
+        String sanitizedName = PrometheusTimeSeries.sanitizeMetricName(sum);
+        assertThat(sanitizedName, equalTo(name + "_total"));
+    }
+
+    @Test
+    public void testSumMetricWithNullUnitAndNullAggregationTemporality() {
+        final String name = RandomStringUtils.randomAlphabetic(10);
+        Sum sum = createSumMetric(name, null, true, null);
+        String sanitizedName = PrometheusTimeSeries.sanitizeMetricName(sum);
+        assertThat(sanitizedName, equalTo(name));
+    }
+
     private Summary createSummaryMetric(final String name, final String unit) {
         List<Quantile> quantiles = Arrays.asList(
             new DefaultQuantile(0.5d, 10d),