diff --git a/src/runner.rs b/src/runner.rs
index 5a9ec84..2d7c53a 100644
--- a/src/runner.rs
+++ b/src/runner.rs
@@ -1109,11 +1109,7 @@ impl FunctionContext {
 			.map(RuntimeValue::default)
 			.collect::<Vec<_>>();
 
-		// TODO: Replace with extend.
-		for local in locals {
-			value_stack.push(local)
-				.map_err(|_| TrapKind::StackOverflow)?;
-		}
+		value_stack.extend(&locals)?;
 
 		self.is_initialized = true;
 		Ok(())
@@ -1263,8 +1259,78 @@ impl ValueStack {
 		Ok(())
 	}
 
+	#[inline]
+	fn extend(&mut self, values: &[RuntimeValue]) -> Result<(), TrapKind> {
+		let avail_len = self.buf.len() - self.sp;
+		let to_copy_len = values.len();
+
+		if to_copy_len <= avail_len {
+		    self.buf[self.sp..(self.sp+to_copy_len)].copy_from_slice(&values[..to_copy_len]);
+		    self.sp += to_copy_len;
+		    Ok(())
+		} else {
+		    Err(TrapKind::StackOverflow)
+		}
+	}
+
 	#[inline]
 	fn len(&self) -> usize {
 		self.sp
 	}
 }
+
+#[cfg(test)]
+mod tests {
+	use super::ValueStack;
+	use value::RuntimeValue;
+
+	#[test]
+	fn test_stack_extend() {
+		let mut stack = ValueStack::with_limit(5);
+		let values = vec![
+			RuntimeValue::I32(1),
+			RuntimeValue::I32(2),
+			RuntimeValue::I32(3),
+			RuntimeValue::I32(4),
+			RuntimeValue::I32(5)
+		];
+
+		assert!(stack.extend(&values).is_ok());
+		assert_eq!(stack.len(), 5);
+
+		assert!(stack.push(RuntimeValue::I32(6)).is_err());
+
+		// check each elements
+		assert_eq!(stack.pop(), RuntimeValue::I32(5));
+		assert_eq!(stack.pop(), RuntimeValue::I32(4));
+		assert_eq!(stack.pop(), RuntimeValue::I32(3));
+		assert_eq!(stack.pop(), RuntimeValue::I32(2));
+		assert_eq!(stack.pop(), RuntimeValue::I32(1));
+
+		assert_eq!(stack.len(), 0);
+	}
+
+	#[test]
+	fn test_stack_extend_overflow() {
+		let mut stack = ValueStack::with_limit(4);
+		let values = vec![
+			RuntimeValue::I32(1),
+			RuntimeValue::I32(2),
+			RuntimeValue::I32(3),
+			RuntimeValue::I32(4),
+			RuntimeValue::I32(5)
+		];
+
+		assert!(stack.extend(&values).is_err());
+		assert_eq!(stack.len(), 0);
+
+		assert!(stack.push(RuntimeValue::I32(6)).is_ok());
+
+		assert_eq!(stack.len(), 1);
+
+		// check each elements
+		assert_eq!(stack.pop(), RuntimeValue::I32(6));
+
+		assert_eq!(stack.len(), 0);
+	}
+}