diff --git a/.circleci/config.yml b/.circleci/config.yml
index 7f2bedc..bae5d00 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -25,7 +25,7 @@ jobs:
             - ".git"
       - run:
           name: config
-          command: meson << parameters.build-config >> . build
+          command: meson << parameters.build-config >> -Dwerror=true . build
       - run:
           name: build
           command: ninja -C build
diff --git a/src/kernel.c b/src/kernel.c
index f816310..435857b 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -23,7 +23,7 @@
  *  center  +-----+-------------------+-----+
  */
 
-double attr_const attr_pure sum_kernel(const conv *map, int x, int y, int width,
+double sum_kernel(const conv *map, int x, int y, int width,
                                        int height) {
 	int fx, fy;
 	const double *g_data;
@@ -77,7 +77,7 @@ double attr_const attr_pure sum_kernel(const conv *map, int x, int y, int width,
 	return v;
 }
 
-static double attr_const attr_pure gaussian(double r, double x, double y) {
+static double attr_const gaussian(double r, double x, double y) {
 	// Formula can be found here:
 	// https://en.wikipedia.org/wiki/Gaussian_blur#Mathematics
 	// Except a special case for r == 0 to produce sharp shadows
diff --git a/src/kernel.h b/src/kernel.h
index fcc5ddf..7864619 100644
--- a/src/kernel.h
+++ b/src/kernel.h
@@ -13,8 +13,7 @@ typedef struct conv {
 
 /// Calculate the sum of a rectangle part of the convolution kernel
 /// the rectangle is defined by top left (x, y), and a size (width x height)
-double attr_const attr_pure sum_kernel(const conv *map, int x, int y, int width,
-                                       int height);
+double attr_const sum_kernel(const conv *map, int x, int y, int width, int height);
 
 /// Create a kernel with gaussian distribution of radius r
 conv *gaussian_kernel(double r);