diff --git a/datetime/src/main/java/com/fasterxml/jackson/datatype/jsr310/ser/key/ZonedDateTimeKeySerializer.java b/datetime/src/main/java/com/fasterxml/jackson/datatype/jsr310/ser/key/ZonedDateTimeKeySerializer.java
index dababc8c..66fef7f8 100644
--- a/datetime/src/main/java/com/fasterxml/jackson/datatype/jsr310/ser/key/ZonedDateTimeKeySerializer.java
+++ b/datetime/src/main/java/com/fasterxml/jackson/datatype/jsr310/ser/key/ZonedDateTimeKeySerializer.java
@@ -9,6 +9,7 @@
 import com.fasterxml.jackson.databind.JsonSerializer;
 import com.fasterxml.jackson.databind.SerializationFeature;
 import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.datatype.jsr310.DecimalUtils;
 
 public class ZonedDateTimeKeySerializer extends JsonSerializer<ZonedDateTime> {
 
@@ -20,15 +21,29 @@ private ZonedDateTimeKeySerializer() {
 
     @Override
     public void serialize(ZonedDateTime value, JsonGenerator gen, SerializerProvider serializers) throws IOException,
-            JsonProcessingException {
+        JsonProcessingException {
         /* [modules-java8#127]: Serialization of timezone data is disabled by default, but can be
          * turned on by enabling `SerializationFeature.WRITE_DATES_WITH_ZONE_ID`
          */
         if (serializers.isEnabled(SerializationFeature.WRITE_DATES_WITH_ZONE_ID)) {
             gen.writeFieldName(DateTimeFormatter.ISO_ZONED_DATE_TIME.format(value));
+        } else if (useTimestamps(serializers)) {
+            if (useNanos(serializers)) {
+                gen.writeFieldName(DecimalUtils.toBigDecimal(value.toEpochSecond(), value.getNano()).toString());
+            } else {
+                gen.writeFieldName(String.valueOf(value.toInstant().toEpochMilli()));
+            }
         } else {
             gen.writeFieldName(DateTimeFormatter.ISO_OFFSET_DATE_TIME.format(value));
         }
     }
 
+    private static boolean useNanos(SerializerProvider serializers) {
+        return serializers.isEnabled(SerializationFeature.WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS);
+    }
+
+    private static boolean useTimestamps(SerializerProvider serializers) {
+        return serializers.isEnabled(SerializationFeature.WRITE_DATE_KEYS_AS_TIMESTAMPS);
+    }
+
 }
diff --git a/datetime/src/test/java/com/fasterxml/jackson/datatype/jsr310/key/ZonedDateTimeAsKeyTest.java b/datetime/src/test/java/com/fasterxml/jackson/datatype/jsr310/key/ZonedDateTimeAsKeyTest.java
index a65d6b08..c0ed5954 100644
--- a/datetime/src/test/java/com/fasterxml/jackson/datatype/jsr310/key/ZonedDateTimeAsKeyTest.java
+++ b/datetime/src/test/java/com/fasterxml/jackson/datatype/jsr310/key/ZonedDateTimeAsKeyTest.java
@@ -9,6 +9,7 @@
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.ObjectReader;
+import com.fasterxml.jackson.databind.SerializationFeature;
 import com.fasterxml.jackson.datatype.jsr310.ModuleTestBase;
 
 import org.junit.Assert;
@@ -20,6 +21,7 @@ public class ZonedDateTimeAsKeyTest extends ModuleTestBase
     };
     private static final ZonedDateTime DATE_TIME_0 = ZonedDateTime.ofInstant(Instant.ofEpochSecond(0), ZoneOffset.UTC);
     private static final String DATE_TIME_0_STRING = "1970-01-01T00:00:00Z";
+    private static final Instant DATE_TIME_0_INSTANT = DATE_TIME_0.toInstant();
 
     private static final ZonedDateTime DATE_TIME_1 = ZonedDateTime.of(
             2015, 3, 14, 9, 26, 53, 590 * 1000 * 1000, ZoneOffset.UTC);
@@ -72,4 +74,21 @@ public void testDeserialization2() throws Exception {
         Assert.assertEquals("Value is incorrect", asMap(DATE_TIME_2_OFFSET, "test"),
                 READER.readValue(mapAsString(DATE_TIME_2_STRING, "test")));
     }
+
+    @Test
+    public void testSerializationToInstantWithNanos() throws Exception {
+        String value = newMapperBuilder().enable(SerializationFeature.WRITE_DATE_KEYS_AS_TIMESTAMPS).build()
+            .writerFor(TYPE_REF).writeValueAsString(asMap(DATE_TIME_1, "test"));
+        Assert.assertEquals("Value is incorrect",
+            mapAsString(String.valueOf(DATE_TIME_1.toEpochSecond()) + '.' + DATE_TIME_1.getNano(), "test"), value);
+    }
+
+    @Test
+    public void testSerializationToInstantWithoutNanos() throws Exception {
+        String value = newMapperBuilder().enable(SerializationFeature.WRITE_DATE_KEYS_AS_TIMESTAMPS)
+            .disable(SerializationFeature.WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS).build()
+            .writerFor(TYPE_REF).writeValueAsString(asMap(DATE_TIME_1, "test"));
+        Assert.assertEquals("Value is incorrect",
+            mapAsString(String.valueOf(DATE_TIME_1.toInstant().toEpochMilli()), "test"), value);
+    }
 }