diff --git a/src/renderers/WebGLRenderer.js b/src/renderers/WebGLRenderer.js
index fd9d36b027c212..22a1d0bbf7d84d 100644
--- a/src/renderers/WebGLRenderer.js
+++ b/src/renderers/WebGLRenderer.js
@@ -3762,7 +3762,13 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 				if ( _gl.checkFramebufferStatus( _gl.FRAMEBUFFER ) === _gl.FRAMEBUFFER_COMPLETE ) {
 
-					_gl.readPixels( x, y, width, height, paramThreeToGL( texture.format ), paramThreeToGL( texture.type ), buffer );
+					// the following if statement ensures valid read requests (no out-of-bounds pixels, see #8604)
+
+					if ( ( x > 0 && x <= ( renderTarget.width - width ) ) && ( y > 0 && y <= ( renderTarget.height - height ) ) ) {
+
+						_gl.readPixels( x, y, width, height, paramThreeToGL( texture.format ), paramThreeToGL( texture.type ), buffer );
+
+					}
 
 				} else {