diff --git a/src/lib.rs b/src/lib.rs
index 6ca3e38..2148c47 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -82,7 +82,7 @@ pub enum CompressedPixelUnpackData<'a> {
     Slice(&'a [u8]),
 }
 
-pub trait HasContext {
+pub trait HasContext : __private::Sealed {
     type Shader: Copy + Clone + Debug + Eq + Hash + Ord + PartialEq + PartialOrd;
     type Program: Copy + Clone + Debug + Eq + Hash + Ord + PartialEq + PartialOrd;
     type Buffer: Copy + Clone + Debug + Eq + Hash + Ord + PartialEq + PartialOrd;
@@ -4175,3 +4175,9 @@ pub const XOR: u32 = 0x1506;
 pub const ZERO: u32 = 0;
 
 pub const ZERO_TO_ONE: u32 = 0x935F;
+
+mod __private {
+    /// Prevents [`HasContext`] from being implemented outside of this crate.
+    #[doc(hidden)]
+    pub trait Sealed {}
+}
diff --git a/src/native.rs b/src/native.rs
index 3604bdb..231fcd6 100644
--- a/src/native.rs
+++ b/src/native.rs
@@ -176,6 +176,8 @@ pub struct NativeUniformLocation(pub native_gl::GLuint);
 #[derive(Copy, Clone, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
 pub struct NativeTransformFeedback(pub NonZeroU32);
 
+impl crate::__private::Sealed for Context {}
+
 impl HasContext for Context {
     type Shader = NativeShader;
     type Program = NativeProgram;
diff --git a/src/web_sys.rs b/src/web_sys.rs
index 1ca7792..4cb4581 100644
--- a/src/web_sys.rs
+++ b/src/web_sys.rs
@@ -1359,6 +1359,8 @@ new_key_type! { pub struct WebRenderbufferKey; }
 new_key_type! { pub struct WebQueryKey; }
 new_key_type! { pub struct WebTransformFeedbackKey; }
 
+impl crate::__private::Sealed for Context {}
+
 impl HasContext for Context {
     type Shader = WebShaderKey;
     type Program = WebProgramKey;