diff --git a/api/include/opentelemetry/trace/default_span.h b/api/include/opentelemetry/trace/default_span.h
index f33f584c6d..e42523637f 100644
--- a/api/include/opentelemetry/trace/default_span.h
+++ b/api/include/opentelemetry/trace/default_span.h
@@ -8,6 +8,7 @@
 #define pass
 OPENTELEMETRY_BEGIN_NAMESPACE
 namespace trace {
+class DefaultTracer;
 class DefaultSpan: public Span {
   public:
     // Returns an invalid span.