diff --git a/packages/ai/src/protocols/cohere-chat.ts b/packages/ai/src/protocols/cohere-chat.ts
index 876d5e297660..a32f9eefc6ae 100644
--- a/packages/ai/src/protocols/cohere-chat.ts
+++ b/packages/ai/src/protocols/cohere-chat.ts
@@ -190,7 +190,7 @@ const fromRequest = Effect.fn("CohereChat.fromRequest")(function* (request: LLMR
         calls.push({ id: part.id, type: "function", function: { name: part.name, arguments: args } })
         continue
       }
-      if (message.role === "user" && part.type === "media" && part.media.mediaType.startsWith("image/")) {
+      if (message.role === "user" && part.type === "media" && part.media.mediaType.toLowerCase().startsWith("image/")) {
         const url =
           ProviderShared.mediaUrl(part.media) ??
           (yield* ProviderShared.requireInlineMedia("Cohere Chat", part.media)).dataUrl
diff --git a/packages/ai/test/provider/cohere.test.ts b/packages/ai/test/provider/cohere.test.ts
index 608c5d247de6..bb41d719ff4a 100644
--- a/packages/ai/test/provider/cohere.test.ts
+++ b/packages/ai/test/provider/cohere.test.ts
@@ -209,6 +209,31 @@ it.effect("Cohere rejects unsupported media instead of silently dropping it", ()
   }),
 )
 
+it.effect("Cohere accepts image media regardless of MIME type casing", () =>
+  Effect.gen(function* () {
+    const prepared = yield* compileRequest(
+      LLM.request({
+        model: cohere.model("command-a-03-2025"),
+        messages: [
+          Message.user([
+            { type: "media", media: Media.base64("aGVsbG8=", "IMAGE/PNG") },
+            { type: "media", media: Media.url("https://files.example/pic.png", { mediaType: "Image/Png" }) },
+          ]),
+        ],
+      }),
+    )
+    expect(prepared.body.messages).toMatchObject([
+      {
+        role: "user",
+        content: [
+          { type: "image_url", image_url: { url: "data:image/png;base64,aGVsbG8=" } },
+          { type: "image_url", image_url: { url: "https://files.example/pic.png" } },
+        ],
+      },
+    ])
+  }),
+)
+
 it.effect("Cohere thinking budgets must be positive integers", () =>
   Effect.gen(function* () {
     const error = yield* compileRequest(