diff --git a/stdlib/src/canvas.rs b/stdlib/src/canvas.rs
index d7dee547..502f5ac3 100644
--- a/stdlib/src/canvas.rs
+++ b/stdlib/src/canvas.rs
@@ -3,7 +3,10 @@ use std::cell::RefCell;
 use std::collections::HashMap;
 use std::rc::Rc;
 use techscript_runtime::{
-    context::RuntimeContext, error::RuntimeError, function::Callable, value::RuntimeValue,
+    context::{Capability, RuntimeContext},
+    error::RuntimeError,
+    function::Callable,
+    value::RuntimeValue,
 };
 
 /// Convert a DslBlockValue to SVG string.
@@ -271,7 +274,7 @@ impl Callable for CanvasFn {
     }
     fn call(
         &self,
-        _ctx: &mut RuntimeContext,
+        ctx: &mut RuntimeContext,
         args: Vec<RuntimeValue>,
     ) -> Result<RuntimeValue, RuntimeError> {
         let mut buf = self.buffer.borrow_mut();
@@ -361,6 +364,15 @@ impl Callable for CanvasFn {
                 Ok(RuntimeValue::Null)
             }
             CanvasOp::Save => {
+                if !ctx.config.capabilities.contains(&Capability::FileSystem) {
+                    return Err(RuntimeError::new(
+                        techscript_runtime::error::RuntimeErrorKind::InvalidOperation(
+                            "FileSystem capability is required to save canvas".to_string(),
+                        ),
+                        None,
+                        None,
+                    ));
+                }
                 let path = args[0].to_string();
                 let content = buf.clone();
                 std::fs::write(&path, &content).map_err(|e| {
@@ -659,7 +671,7 @@ impl StdlibRegistry {
                 name: "std.canvas".to_string(),
                 version: "1.0.0".to_string(),
                 exports,
-                required_capabilities: Vec::new(),
+                required_capabilities: vec![Capability::FileSystem],
             },
         );
     }