diff --git a/opentelemetry-api/src/opentelemetry/trace/span.py b/opentelemetry-api/src/opentelemetry/trace/span.py
index b0cda475e2..7bb6e1e543 100644
--- a/opentelemetry-api/src/opentelemetry/trace/span.py
+++ b/opentelemetry-api/src/opentelemetry/trace/span.py
@@ -21,7 +21,7 @@
 
 _KEY_FORMAT = (
     r"[a-z][_0-9a-z\-\*\/]{0,255}|"
-    r"[a-z0-9][_0-9a-z\-\*\/]{0,240}@[a-z][_0-9a-z\-\*\/]{0,13}"
+    r"[a-z0-9][_0-9a-z\-\*\/]{0,240}@[a-z][_0-9a-z\-\*\/]{0,14}"
 )
 _KEY_PATTERN = re.compile(_KEY_FORMAT)