diff --git a/effects/dropshadow.frag b/effects/dropshadow.frag
index dc41d000f..1bed6e491 100644
--- a/effects/dropshadow.frag
+++ b/effects/dropshadow.frag
@@ -4,7 +4,7 @@ uniform sampler2D image;
 
 uniform vec2 resolution;
 
-uniform bool shadow;
+uniform int shadow;
 uniform vec3 shadowcolor;
 uniform float shadowsoftness;
 uniform float shadowopacity;
@@ -14,8 +14,7 @@ varying vec2 vTexCoord;
 
 void main(void) {
 	vec4 master_px = texture2D(image, vTexCoord);
-	if (shadow) {
-
+	if (shadow == 1) {
 		vec2 shadow_dist = vec2(shadowdistance)/resolution;
 
 		float shadow_opacity = 0.01*shadowopacity;
diff --git a/project/effect.cpp b/project/effect.cpp
index e1dd0942a..cf0c495ea 100644
--- a/project/effect.cpp
+++ b/project/effect.cpp
@@ -820,9 +820,18 @@ void Effect::open() {
 		} else {
 			glslProgram = new QOpenGLShaderProgram();
 			validate_meta_path();
-			if (!vertPath.isEmpty()) glslProgram->addShaderFromSourceFile(QOpenGLShader::Vertex, meta->path + "/" + vertPath);
-			if (!fragPath.isEmpty()) glslProgram->addShaderFromSourceFile(QOpenGLShader::Fragment, meta->path + "/" + fragPath);
-			glslProgram->link();
+			bool glsl_compiled = true;
+			if (!vertPath.isEmpty()) {
+				if (!glslProgram->addShaderFromSourceFile(QOpenGLShader::Vertex, meta->path + "/" + vertPath)) {
+					glsl_compiled = false;
+				}
+			}
+			if (!fragPath.isEmpty()) {
+				if (!glslProgram->addShaderFromSourceFile(QOpenGLShader::Fragment, meta->path + "/" + fragPath)) {
+					glsl_compiled = false;
+				}
+			}
+			if (glsl_compiled) glslProgram->link();
 			isOpen = true;
 		}
 	} else {
@@ -846,12 +855,16 @@ void Effect::close() {
 	isOpen = false;
 }
 
+bool Effect::is_glsl_linked() {
+	return glslProgram != NULL && glslProgram->isLinked();
+}
+
 void Effect::startEffect() {
 	if (!isOpen) {
 		open();
 		dout << "[WARNING] Tried to start a closed effect - opening";
 	}
-	if (enable_shader) bound = glslProgram->bind();
+	if (enable_shader && glslProgram->isLinked()) bound = glslProgram->bind();
 }
 
 void Effect::endEffect() {
diff --git a/project/effect.h b/project/effect.h
index 7c48fd81f..d1a2cb4b2 100644
--- a/project/effect.h
+++ b/project/effect.h
@@ -142,6 +142,7 @@ public:
 	bool is_open();
 	void open();
 	void close();
+	bool is_glsl_linked();
 	virtual void startEffect();
 	virtual void endEffect();
 
diff --git a/ui/viewerwidget.cpp b/ui/viewerwidget.cpp
index 659b344f9..f46b8c1c3 100644
--- a/ui/viewerwidget.cpp
+++ b/ui/viewerwidget.cpp
@@ -189,7 +189,7 @@ void ViewerWidget::initializeGL() {
 //}
 
 void ViewerWidget::paintEvent(QPaintEvent *e) {
-    if (!rendering && context()->thread() == this->thread()) {
+	if (!rendering && context()->thread() == this->thread()) {
 		makeCurrent();
 		QOpenGLWidget::paintEvent(e);
 	}
@@ -429,7 +429,7 @@ void ViewerWidget::process_effect(Clip* c, Effect* e, double timecode, GLTexture
 		}
 		if (e->enable_shader || e->enable_superimpose) {
 			e->startEffect();
-			if (e->enable_shader) {
+			if (e->enable_shader && e->is_glsl_linked()) {
 				e->process_shader(timecode, coords);
 				composite_texture = draw_clip(c->fbo[fbo_switcher], composite_texture, true);
 				fbo_switcher = !fbo_switcher;