diff --git a/sentry/src/main/java/io/sentry/SentryTracer.java b/sentry/src/main/java/io/sentry/SentryTracer.java
index e3cc1498e5..48a1f5ec63 100644
--- a/sentry/src/main/java/io/sentry/SentryTracer.java
+++ b/sentry/src/main/java/io/sentry/SentryTracer.java
@@ -7,6 +7,7 @@
 import io.sentry.protocol.TransactionNameSource;
 import io.sentry.protocol.User;
 import io.sentry.util.Objects;
+import io.sentry.util.thread.MainThreadChecker;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.ListIterator;
@@ -384,6 +385,8 @@ private ISpan createChild(
               }
             });
     span.setDescription(description);
+    span.setData(
+        SpanDataConvention.BLOCKED_MAIN_THREAD_KEY, MainThreadChecker.getInstance().isMainThread());
     this.children.add(span);
     return span;
   }
diff --git a/sentry/src/test/java/io/sentry/SentryTracerTest.kt b/sentry/src/test/java/io/sentry/SentryTracerTest.kt
index ee698af6c0..65ae250790 100644
--- a/sentry/src/test/java/io/sentry/SentryTracerTest.kt
+++ b/sentry/src/test/java/io/sentry/SentryTracerTest.kt
@@ -1236,4 +1236,10 @@ class SentryTracerTest {
         assertTrue(tracer.isFinished)
         verify(fixture.hub).captureTransaction(any(), anyOrNull(), anyOrNull(), anyOrNull())
     }
+
+    @Test
+    fun `when a span is launched, the main thread flag is set as span data`() {
+        val tracer = fixture.getSut()
+        assertNotNull(tracer.startChild("span.op").getData(SpanDataConvention.BLOCKED_MAIN_THREAD_KEY))
+    }
 }