diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index b74bfb33c..dc726321d 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -11,6 +11,7 @@
 - Fixed MCP OAuth sign-in accepting an authorization response whose `iss` parameter names another authorization server; the code is now rejected before it is exchanged (RFC 9207).
 - Fixed MCP OAuth sign-in failing with `Invalid scope` when the token response contains `"scope": ""`, and similar failures for other empty or `null` optional OAuth fields ([#10266](https://github.com/earendil-works/pi/issues/10266)).
 - Fixed the sign-in URL printed by `/mcp login` not being clickable when it wraps ([#10186](https://github.com/earendil-works/pi/issues/10186)).
+- Fixed `--provider` without `--model` being silently ignored and running the default model from another provider; it now fails with an error ([#10236](https://github.com/earendil-works/pi/issues/10236)).
 
 ## [0.99.2] - 2026-09-30
 
diff --git a/packages/coding-agent/docs/cli.md b/packages/coding-agent/docs/cli.md
index 8e1300390..832642aa8 100644
--- a/packages/coding-agent/docs/cli.md
+++ b/packages/coding-agent/docs/cli.md
@@ -61,7 +61,7 @@ pi --model sonnet:high
 See [Choose a Model](models.md) for model selection and [Provider Authentication](providers.md) for credentials.
 
 - `--provider <name>`<br>
-  Restricts `--model` lookup to one provider.
+  Restricts `--model` lookup to one provider. It requires `--model`.
 - `--model <pattern>`<br>
   Selects by exact ID or fuzzy ID/name match. It accepts `provider/id` and an optional `:<thinking>` suffix.
 - `--api-key <key>`<br>
diff --git a/packages/coding-agent/src/cli/args.ts b/packages/coding-agent/src/cli/args.ts
index 17f27513f..b3d58d7cb 100644
--- a/packages/coding-agent/src/cli/args.ts
+++ b/packages/coding-agent/src/cli/args.ts
@@ -286,7 +286,7 @@ ${chalk.bold("Commands:")}
   ${APP_NAME} <command> --help          Show help for install/remove/uninstall/update/list/config/auth/mcp
 
 ${chalk.bold("Options:")}
-  --provider <name>              Provider name (default: google)
+  --provider <name>              Provider to search for --model (requires --model)
   --model <pattern>              Model pattern or ID (supports "provider/id" and optional ":<thinking>")
   --api-key <key>                API key (defaults to env vars)
   --system-prompt <text>         System prompt (default: coding assistant prompt)
diff --git a/packages/coding-agent/src/main.ts b/packages/coding-agent/src/main.ts
index ee2679a43..d9c6ce33c 100644
--- a/packages/coding-agent/src/main.ts
+++ b/packages/coding-agent/src/main.ts
@@ -466,6 +466,12 @@ function buildSessionOptions(
 	// Model from CLI
 	// - supports --provider <name> --model <pattern>
 	// - supports --model <provider>/<pattern>
+	if (parsed.provider && !parsed.model) {
+		diagnostics.push({
+			type: "error",
+			message: `--provider requires --model (for example: --provider ${parsed.provider} --model <pattern>)`,
+		});
+	}
 	if (parsed.model) {
 		const resolved = resolveCliModel({
 			cliProvider: parsed.provider,