diff --git a/packages/opencode/src/tool/webfetch.ts b/packages/opencode/src/tool/webfetch.ts
index 66344c67d96..96d14900e40 100644
--- a/packages/opencode/src/tool/webfetch.ts
+++ b/packages/opencode/src/tool/webfetch.ts
@@ -108,7 +108,7 @@ export const WebFetchTool = Tool.define(
           const contentType = response.headers["content-type"] || ""
           const mime = contentType.split(";")[0]?.trim().toLowerCase() || ""
           const title = `${url} (${contentType})` // kilocode_change
-
+          if (isIconMimeType(mime)) throw new Error(`Unsupported image format: ${mime}`) // kilocode_change
           if (isImageAttachment(mime)) {
             const base64Content = Buffer.from(arrayBuffer).toString("base64")
             return {
@@ -125,16 +125,6 @@ export const WebFetchTool = Tool.define(
             }
           }
 
-          // kilocode_change start
-          if (isIconMimeType(mime)) {
-            return {
-              title,
-              output: `Unsupported image format: ${mime}.`,
-              metadata: {},
-            }
-          }
-          // kilocode_change end
-
           const content = new TextDecoder().decode(arrayBuffer)
 
           // Handle content based on requested format and actual content type
diff --git a/packages/opencode/test/tool/webfetch.test.ts b/packages/opencode/test/tool/webfetch.test.ts
index e7df83c4f7b..20a48f445c5 100644
--- a/packages/opencode/test/tool/webfetch.test.ts
+++ b/packages/opencode/test/tool/webfetch.test.ts
@@ -91,9 +91,9 @@ describe("tool.webfetch", () => {
         await WithInstance.provide({
           directory: projectRoot,
           fn: async () => {
-            const result = await exec({ url: new URL("/favicon.ico", url).toString(), format: "markdown" })
-            expect(result.output).toContain(`Unsupported image format: ${mime}`)
-            expect(result.attachments).toBeUndefined()
+            await expect(exec({ url: new URL("/favicon.ico", url).toString(), format: "markdown" })).rejects.toThrow(
+              `Unsupported image format: ${mime}`,
+            )
           },
         })
       },