diff --git a/api/app/clients/prompts/formatMessages.js b/api/app/clients/prompts/formatMessages.js
index e288b28caa..5489a8ae01 100644
--- a/api/app/clients/prompts/formatMessages.js
+++ b/api/app/clients/prompts/formatMessages.js
@@ -44,6 +44,16 @@ const formatMessage = ({ message, userName, assistantName, langChain = false })
     formattedMessage.name = assistantName;
   }
 
+  if (formattedMessage.name) {
+    // Conform to API regex: ^[a-zA-Z0-9_-]{1,64}$
+    // https://community.openai.com/t/the-format-of-the-name-field-in-the-documentation-is-incorrect/175684/2
+    formattedMessage.name = formattedMessage.name.replace(/[^a-zA-Z0-9_-]/g, '_');
+
+    if (formattedMessage.name.length > 64) {
+      formattedMessage.name = formattedMessage.name.substring(0, 64);
+    }
+  }
+
   if (!langChain) {
     return formattedMessage;
   }
diff --git a/api/app/clients/prompts/formatMessages.spec.js b/api/app/clients/prompts/formatMessages.spec.js
index 16c400739e..0497e4c47a 100644
--- a/api/app/clients/prompts/formatMessages.spec.js
+++ b/api/app/clients/prompts/formatMessages.spec.js
@@ -18,6 +18,36 @@ describe('formatMessage', () => {
     });
   });
 
+  it('sanitizes the name by replacing invalid characters (per OpenAI)', () => {
+    const input = {
+      message: {
+        sender: 'user',
+        text: 'Hello',
+      },
+      userName: ' John$Doe@Example! ',
+    };
+    const result = formatMessage(input);
+    expect(result).toEqual({
+      role: 'user',
+      content: 'Hello',
+      name: '_John_Doe_Example__',
+    });
+  });
+
+  it('trims the name to a maximum length of 64 characters', () => {
+    const longName = 'a'.repeat(100);
+    const input = {
+      message: {
+        sender: 'user',
+        text: 'Hello',
+      },
+      userName: longName,
+    };
+    const result = formatMessage(input);
+    expect(result.name.length).toBe(64);
+    expect(result.name).toBe('a'.repeat(64));
+  });
+
   it('formats a realistic user message', () => {
     const input = {
       message: {
diff --git a/api/app/clients/specs/OpenAIClient.test.js b/api/app/clients/specs/OpenAIClient.test.js
index 6dc4123a6a..7257aec36a 100644
--- a/api/app/clients/specs/OpenAIClient.test.js
+++ b/api/app/clients/specs/OpenAIClient.test.js
@@ -221,7 +221,7 @@ describe('OpenAIClient', () => {
         isChatCompletion: true,
       });
       const hasUserWithName = result.prompt.some(
-        (item) => item.role === 'user' && item.name === 'Test User',
+        (item) => item.role === 'user' && item.name === 'Test_User',
       );
       expect(hasUserWithName).toBe(true);
     });