diff --git a/src/Sentry/TransactionTracer.cs b/src/Sentry/TransactionTracer.cs
index a133a97184..cfb6cb8b15 100644
--- a/src/Sentry/TransactionTracer.cs
+++ b/src/Sentry/TransactionTracer.cs
@@ -324,16 +324,16 @@ internal ISpan StartChild(SpanId? spanId, SpanId parentSpanId, string operation,
 
     private void AddChildSpan(SpanTracer span)
     {
-        var isOutOfLimit = _spans.Count >= SpanLimit;
-        span.IsSampled = isOutOfLimit ? false : IsSampled;
-        if (isOutOfLimit)
-        {
-            _options?.LogDebug("Discarding child span '{0}' due to {1} span limit", SpanId, SpanLimit);
-            return;
-        }
-
         lock (_finishLock)
         {
+            var isOutOfLimit = _spans.Count >= SpanLimit;
+            span.IsSampled = isOutOfLimit ? false : IsSampled;
+            if (isOutOfLimit)
+            {
+                _options?.LogDebug("Discarding child span '{0}' due to {1} span limit", SpanId, SpanLimit);
+                return;
+            }
+
             if (_hasFinished)
             {
                 _options?.LogDebug("Discarding child span '{0}' as the trace has already finished", SpanId);
diff --git a/test/Sentry.Tests/Protocol/SentryTransactionTests.cs b/test/Sentry.Tests/Protocol/SentryTransactionTests.cs
index e774e7a0f3..8ccca8ff84 100644
--- a/test/Sentry.Tests/Protocol/SentryTransactionTests.cs
+++ b/test/Sentry.Tests/Protocol/SentryTransactionTests.cs
@@ -350,6 +350,21 @@ public void StartChild_Limit_Maintained()
         spans.Count(s => s.IsSampled == true).Should().Be(1000);
     }
 
+    [Fact]
+    public void StartChild_Limit_Maintained_Concurrently()
+    {
+        // Arrange
+        var transaction = new TransactionTracer(DisabledHub.Instance, "my name", "my op");
+        var spans = new ConcurrentBag<ISpan>();
+
+        // Act
+        Parallel.For(0, 5000, i => spans.Add(transaction.StartChild("span " + i)));
+
+        // Assert
+        transaction.Spans.Should().HaveCount(1000);
+        spans.Count(s => s.IsSampled == true).Should().Be(1000);
+    }
+
     [Fact]
     public void StartChild_SamplingInherited_True()
     {