diff --git a/components/script/dom/webglprogram.rs b/components/script/dom/webglprogram.rs
index 6cc122cf459..504a13ec339 100644
--- a/components/script/dom/webglprogram.rs
+++ b/components/script/dom/webglprogram.rs
@@ -68,6 +68,14 @@ impl WebGLProgram {
         if !self.is_deleted.get() {
             self.is_deleted.set(true);
             let _ = self.renderer.send(CanvasMsg::WebGL(WebGLCommand::DeleteProgram(self.id)));
+
+            if let Some(shader) = self.fragment_shader.get() {
+                shader.decrement_attached_counter();
+            }
+
+            if let Some(shader) = self.vertex_shader.get() {
+                shader.decrement_attached_counter();
+            }
         }
     }
 
@@ -118,6 +126,7 @@ impl WebGLProgram {
         }
 
         shader_slot.set(Some(shader));
+        shader.increment_attached_counter();
 
         self.renderer.send(CanvasMsg::WebGL(WebGLCommand::AttachShader(self.id, shader.id()))).unwrap();
 
@@ -144,6 +153,7 @@ impl WebGLProgram {
         }
 
         shader_slot.set(None);
+        shader.decrement_attached_counter();
 
         self.renderer.send(CanvasMsg::WebGL(WebGLCommand::DetachShader(self.id, shader.id()))).unwrap();
 
diff --git a/components/script/dom/webglrenderingcontext.rs b/components/script/dom/webglrenderingcontext.rs
index 36a8a4bb3b2..70b98ce06cd 100644
--- a/components/script/dom/webglrenderingcontext.rs
+++ b/components/script/dom/webglrenderingcontext.rs
@@ -1157,6 +1157,16 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
             .unwrap()
     }
 
+    // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.9
+    fn IsShader(&self, shader: Option<&WebGLShader>) -> bool {
+        shader.map_or(false, |s| !s.is_deleted() || s.is_attached())
+    }
+
+    // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.8
+    fn IsTexture(&self, texture: Option<&WebGLTexture>) -> bool {
+        texture.map_or(false, |tex| tex.target().is_some() && !tex.is_deleted())
+    }
+
     // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.3
     fn LineWidth(&self, width: f32) {
         if width.is_nan() || width <= 0f32 {
diff --git a/components/script/dom/webglshader.rs b/components/script/dom/webglshader.rs
index eb930a69f13..c166fbcf46d 100644
--- a/components/script/dom/webglshader.rs
+++ b/components/script/dom/webglshader.rs
@@ -32,6 +32,7 @@ pub struct WebGLShader {
     source: DOMRefCell<Option<DOMString>>,
     info_log: DOMRefCell<Option<String>>,
     is_deleted: Cell<bool>,
+    attached_counter: Cell<u32>,
     compilation_status: Cell<ShaderCompilationStatus>,
     #[ignore_heap_size_of = "Defined in ipc-channel"]
     renderer: IpcSender<CanvasMsg>,
@@ -55,6 +56,7 @@ impl WebGLShader {
             source: DOMRefCell::new(None),
             info_log: DOMRefCell::new(None),
             is_deleted: Cell::new(false),
+            attached_counter: Cell::new(0),
             compilation_status: Cell::new(ShaderCompilationStatus::NotCompiled),
             renderer: renderer,
         }
@@ -126,6 +128,7 @@ impl WebGLShader {
 
     /// Mark this shader as deleted (if it wasn't previously)
     /// and delete it as if calling glDeleteShader.
+    /// Currently does not check if shader is attached
     pub fn delete(&self) {
         if !self.is_deleted.get() {
             self.is_deleted.set(true);
@@ -133,6 +136,23 @@ impl WebGLShader {
         }
     }
 
+    pub fn is_deleted(&self) -> bool {
+        self.is_deleted.get()
+    }
+
+    pub fn is_attached(&self) -> bool {
+        self.attached_counter.get() > 0
+    }
+
+    pub fn increment_attached_counter(&self) {
+        self.attached_counter.set(self.attached_counter.get() + 1);
+    }
+
+    pub fn decrement_attached_counter(&self) {
+        assert!(self.attached_counter.get() > 0);
+        self.attached_counter.set(self.attached_counter.get() - 1);
+    }
+
     /// glGetShaderInfoLog
     pub fn info_log(&self) -> Option<String> {
         self.info_log.borrow().clone()
@@ -162,6 +182,7 @@ impl WebGLShader {
 
 impl Drop for WebGLShader {
     fn drop(&mut self) {
+        assert!(self.attached_counter.get() == 0);
         self.delete();
     }
 }
diff --git a/components/script/dom/webgltexture.rs b/components/script/dom/webgltexture.rs
index e92435ce304..df636a1db59 100644
--- a/components/script/dom/webgltexture.rs
+++ b/components/script/dom/webgltexture.rs
@@ -176,6 +176,14 @@ impl WebGLTexture {
         }
     }
 
+    pub fn is_deleted(&self) -> bool {
+        self.is_deleted.get()
+    }
+
+    pub fn target(&self) -> Option<u32> {
+        self.target.get()
+    }
+
     /// We have to follow the conversion rules for GLES 2.0. See:
     ///   https://www.khronos.org/webgl/public-mailing-list/archives/1008/msg00014.html
     ///
diff --git a/components/script/dom/webidls/WebGLRenderingContext.webidl b/components/script/dom/webidls/WebGLRenderingContext.webidl
index 4b29660b190..f46da97fd65 100644
--- a/components/script/dom/webidls/WebGLRenderingContext.webidl
+++ b/components/script/dom/webidls/WebGLRenderingContext.webidl
@@ -605,8 +605,8 @@ interface WebGLRenderingContextBase
     //[WebGLHandlesContextLoss] GLboolean isFramebuffer(WebGLFramebuffer? framebuffer);
     //[WebGLHandlesContextLoss] GLboolean isProgram(WebGLProgram? program);
     //[WebGLHandlesContextLoss] GLboolean isRenderbuffer(WebGLRenderbuffer? renderbuffer);
-    //[WebGLHandlesContextLoss] GLboolean isShader(WebGLShader? shader);
-    //[WebGLHandlesContextLoss] GLboolean isTexture(WebGLTexture? texture);
+    [WebGLHandlesContextLoss] GLboolean isShader(WebGLShader? shader);
+    [WebGLHandlesContextLoss] GLboolean isTexture(WebGLTexture? texture);
     void lineWidth(GLfloat width);
     void linkProgram(WebGLProgram? program);
     void pixelStorei(GLenum pname, GLint param);