diff --git a/dd-trace-ot/src/main/java/datadog/trace/common/serialization/MsgpackFormatWriter.java b/dd-trace-ot/src/main/java/datadog/trace/common/serialization/MsgpackFormatWriter.java
index ca5579da7e..f892c80f6b 100644
--- a/dd-trace-ot/src/main/java/datadog/trace/common/serialization/MsgpackFormatWriter.java
+++ b/dd-trace-ot/src/main/java/datadog/trace/common/serialization/MsgpackFormatWriter.java
@@ -32,7 +32,11 @@ public class MsgpackFormatWriter extends FormatWriter<MessagePacker> {
   public void writeString(final String key, final String value, final MessagePacker destination)
       throws IOException {
     destination.packString(key);
-    destination.packString(value);
+    if (value == null) {
+      destination.packNil();
+    } else {
+      destination.packString(value);
+    }
   }
 
   @Override
@@ -82,6 +86,10 @@ public class MsgpackFormatWriter extends FormatWriter<MessagePacker> {
       final String key, final BigInteger value, final MessagePacker destination)
       throws IOException {
     destination.packString(key);
-    destination.packBigInteger(value);
+    if (value == null) {
+      destination.packNil();
+    } else {
+      destination.packBigInteger(value);
+    }
   }
 }
diff --git a/dd-trace-ot/src/test/groovy/datadog/opentracing/DDSpanSerializationTest.groovy b/dd-trace-ot/src/test/groovy/datadog/opentracing/DDSpanSerializationTest.groovy
index 8b5e04a336..7e3ee405b2 100644
--- a/dd-trace-ot/src/test/groovy/datadog/opentracing/DDSpanSerializationTest.groovy
+++ b/dd-trace-ot/src/test/groovy/datadog/opentracing/DDSpanSerializationTest.groovy
@@ -33,7 +33,7 @@ class DDSpanSerializationTest extends DDSpecification {
       parent_id: 0l,
       start    : 100000,
       duration : 33000,
-      type     : "type",
+      type     : spanType,
       error    : 0,
       metrics  : metrics,
       meta     : [
@@ -58,7 +58,7 @@ class DDSpanSerializationTest extends DDSpecification {
         null,
         ["a-baggage": "value"],
         false,
-        "type",
+        spanType,
         ["k1": "v1"],
         new PendingTrace(tracer, 1G, [:]),
         tracer)
@@ -73,9 +73,9 @@ class DDSpanSerializationTest extends DDSpecification {
     actualTree == expectedTree
 
     where:
-    samplingPriority              | _
-    PrioritySampling.SAMPLER_KEEP | _
-    PrioritySampling.UNSET        | _
+    samplingPriority              | spanType
+    PrioritySampling.SAMPLER_KEEP | null
+    PrioritySampling.UNSET        | "some-type"
   }
 
   def "serialize trace/span with id #value as int"() {
@@ -93,7 +93,7 @@ class DDSpanSerializationTest extends DDSpecification {
       null,
       Collections.emptyMap(),
       false,
-      "fakeType",
+      spanType,
       Collections.emptyMap(),
       new PendingTrace(tracer, 1G, [:]),
       tracer)
@@ -122,12 +122,12 @@ class DDSpanSerializationTest extends DDSpecification {
     }
 
     where:
-    value                                           | _
-    0G                                              | _
-    1G                                              | _
-    8223372036854775807G                            | _
-    BigInteger.valueOf(Long.MAX_VALUE).subtract(1G) | _
-    BigInteger.valueOf(Long.MAX_VALUE).add(1G)      | _
-    2G.pow(64).subtract(1G)                         | _
+    value                                           | spanType
+    0G                                              | null
+    1G                                              | "some-type"
+    8223372036854775807G                            | null
+    BigInteger.valueOf(Long.MAX_VALUE).subtract(1G) | "some-type"
+    BigInteger.valueOf(Long.MAX_VALUE).add(1G)      | null
+    2G.pow(64).subtract(1G)                         | "some-type"
   }
 }