diff --git a/sdk/eventhub/azure-eventhub/CHANGELOG.md b/sdk/eventhub/azure-eventhub/CHANGELOG.md
index b7b15068be25..17dd48cc3c51 100644
--- a/sdk/eventhub/azure-eventhub/CHANGELOG.md
+++ b/sdk/eventhub/azure-eventhub/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Release History
 
+## 5.4.1 (Unreleased)
+
+**Bug Fixes**
+
+- Fixed bug that custom user agent string should be put in front of the built-in user agent string instead of being appended.
+
 ## 5.4.0 (2021-04-07)
 
 This version follows from version 5.3.1, rather than 5.4.0b1 so that the preview idempotent producer feature is not included.
diff --git a/sdk/eventhub/azure-eventhub/azure/eventhub/_consumer_client.py b/sdk/eventhub/azure-eventhub/azure/eventhub/_consumer_client.py
index b8de8ad5ad03..2654715e5f58 100644
--- a/sdk/eventhub/azure-eventhub/azure/eventhub/_consumer_client.py
+++ b/sdk/eventhub/azure-eventhub/azure/eventhub/_consumer_client.py
@@ -62,7 +62,7 @@ class EventHubConsumerClient(ClientBase):
     :keyword bool logging_enable: Whether to output network trace logs to the logger. Default is `False`.
     :keyword float auth_timeout: The time in seconds to wait for a token to be authorized by the service.
      The default value is 60 seconds. If set to 0, no timeout will be enforced from the client.
-    :keyword str user_agent: The user agent that should be appended to the built-in user agent string.
+    :keyword str user_agent: If specified, this will be added in front of the user agent string.
     :keyword int retry_total: The total number of attempts to redo a failed operation when an error occurs.
      Default value is 3. The context of `retry_total` in receiving is special: The `receive` method is implemented
      by a while-loop calling internal receive method in each iteration. In the `receive` case,
@@ -209,7 +209,7 @@ def from_connection_string(cls, conn_str, consumer_group, **kwargs):
          Additionally the following keys may also be present: `'username', 'password'`.
         :keyword float auth_timeout: The time in seconds to wait for a token to be authorized by the service.
          The default value is 60 seconds. If set to 0, no timeout will be enforced from the client.
-        :keyword str user_agent: The user agent that should be appended to the built-in user agent string.
+        :keyword str user_agent: If specified, this will be added in front of the user agent string.
         :keyword int retry_total: The total number of attempts to redo a failed operation when an error occurs.
          Default value is 3. The context of `retry_total` in receiving is special: The `receive` method is implemented
          by a while-loop calling internal receive method in each iteration. In the `receive` case,
diff --git a/sdk/eventhub/azure-eventhub/azure/eventhub/_producer_client.py b/sdk/eventhub/azure-eventhub/azure/eventhub/_producer_client.py
index b9c40ba804a8..58872de05b43 100644
--- a/sdk/eventhub/azure-eventhub/azure/eventhub/_producer_client.py
+++ b/sdk/eventhub/azure-eventhub/azure/eventhub/_producer_client.py
@@ -36,7 +36,7 @@ class EventHubProducerClient(ClientBase):
     :keyword bool logging_enable: Whether to output network trace logs to the logger. Default is `False`.
     :keyword float auth_timeout: The time in seconds to wait for a token to be authorized by the service.
      The default value is 60 seconds. If set to 0, no timeout will be enforced from the client.
-    :keyword str user_agent: The user agent that should be appended to the built-in user agent string.
+    :keyword str user_agent: If specified, this will be added in front of the user agent string.
     :keyword int retry_total: The total number of attempts to redo a failed operation when an error occurs. Default
      value is 3.
     :keyword float idle_timeout: Timeout, in seconds, after which this client will close the underlying connection
@@ -171,7 +171,7 @@ def from_connection_string(cls, conn_str, **kwargs):
          Additionally the following keys may also be present: `'username', 'password'`.
         :keyword float auth_timeout: The time in seconds to wait for a token to be authorized by the service.
          The default value is 60 seconds. If set to 0, no timeout will be enforced from the client.
-        :keyword str user_agent: The user agent that should be appended to the built-in user agent string.
+        :keyword str user_agent: If specified, this will be added in front of the user agent string.
         :keyword int retry_total: The total number of attempts to redo a failed operation when an error occurs.
          Default value is 3.
         :keyword float idle_timeout: Timeout, in seconds, after which this client will close the underlying connection
diff --git a/sdk/eventhub/azure-eventhub/azure/eventhub/_utils.py b/sdk/eventhub/azure-eventhub/azure/eventhub/_utils.py
index 77132260b78c..9b7a5b18efc0 100644
--- a/sdk/eventhub/azure-eventhub/azure/eventhub/_utils.py
+++ b/sdk/eventhub/azure-eventhub/azure/eventhub/_utils.py
@@ -91,7 +91,7 @@ def create_properties(user_agent=None):
         USER_AGENT_PREFIX, VERSION, framework, platform_str
     )
     if user_agent:
-        final_user_agent = "{} {}".format(final_user_agent, user_agent)
+        final_user_agent = "{} {}".format(user_agent, final_user_agent)
 
     if len(final_user_agent) > MAX_USER_AGENT_LENGTH:
         raise ValueError(
diff --git a/sdk/eventhub/azure-eventhub/azure/eventhub/_version.py b/sdk/eventhub/azure-eventhub/azure/eventhub/_version.py
index 9f5574c56b5c..2f51b9a42da7 100644
--- a/sdk/eventhub/azure-eventhub/azure/eventhub/_version.py
+++ b/sdk/eventhub/azure-eventhub/azure/eventhub/_version.py
@@ -3,4 +3,4 @@
 # Licensed under the MIT License.
 # ------------------------------------
 
-VERSION = "5.4.0"
+VERSION = "5.4.1"
diff --git a/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_consumer_client_async.py b/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_consumer_client_async.py
index 3e95d8384420..55b979d05114 100644
--- a/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_consumer_client_async.py
+++ b/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_consumer_client_async.py
@@ -69,7 +69,7 @@ class EventHubConsumerClient(ClientBaseAsync):
     :keyword bool logging_enable: Whether to output network trace logs to the logger. Default is `False`.
     :keyword float auth_timeout: The time in seconds to wait for a token to be authorized by the service.
      The default value is 60 seconds. If set to 0, no timeout will be enforced from the client.
-    :keyword str user_agent: The user agent that should be appended to the built-in user agent string.
+    :keyword str user_agent: If specified, this will be added in front of the user agent string.
     :keyword int retry_total: The total number of attempts to redo a failed operation when an error occurs.
      Default value is 3. The context of `retry_total` in receiving is special: The `receive` method is implemented
      by a while-loop calling internal receive method in each iteration. In the `receive` case,
@@ -229,7 +229,7 @@ def from_connection_string(
          Additionally the following keys may also be present: `'username', 'password'`.
         :keyword float auth_timeout: The time in seconds to wait for a token to be authorized by the service.
          The default value is 60 seconds. If set to 0, no timeout will be enforced from the client.
-        :keyword str user_agent: The user agent that should be appended to the built-in user agent string.
+        :keyword str user_agent: If specified, this will be added in front of the user agent string.
         :keyword int retry_total: The total number of attempts to redo a failed operation when an error occurs.
          Default value is 3. The context of `retry_total` in receiving is special: The `receive` method is implemented
          by a while-loop calling internal receive method in each iteration. In the `receive` case,
diff --git a/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_producer_client_async.py b/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_producer_client_async.py
index fa1c92506099..199ede1e771c 100644
--- a/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_producer_client_async.py
+++ b/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_producer_client_async.py
@@ -39,7 +39,7 @@ class EventHubProducerClient(ClientBaseAsync):
     :keyword bool logging_enable: Whether to output network trace logs to the logger. Default is `False`.
     :keyword float auth_timeout: The time in seconds to wait for a token to be authorized by the service.
      The default value is 60 seconds. If set to 0, no timeout will be enforced from the client.
-    :keyword str user_agent: The user agent that should be appended to the built-in user agent string.
+    :keyword str user_agent: If specified, this will be added in front of the user agent string.
     :keyword int retry_total: The total number of attempts to redo a failed operation when an error occurs. Default
      value is 3.
     :keyword float idle_timeout: Timeout, in seconds, after which this client will close the underlying connection
@@ -189,7 +189,7 @@ def from_connection_string(
          Additionally the following keys may also be present: `'username', 'password'`.
         :keyword float auth_timeout: The time in seconds to wait for a token to be authorized by the service.
          The default value is 60 seconds. If set to 0, no timeout will be enforced from the client.
-        :keyword str user_agent: The user agent that should be appended to the built-in user agent string.
+        :keyword str user_agent: If specified, this will be added in front of the user agent string.
         :keyword int retry_total: The total number of attempts to redo a failed operation when an error occurs.
          Default value is 3.
         :keyword float idle_timeout: Timeout, in seconds, after which this client will close the underlying connection