diff --git a/.cirrus.yml b/.cirrus.yml
index 65c7c13..f314478 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -10,8 +10,7 @@ main_freebsd_task:
     - pkg install --yes autoconf automake
   main_build_script:
     - ./autogen.sh
-    # FIXME: -Werror: unknown warning option '-Wno-cast-function-type'
-    - ./configure --enable-tests --disable-werror CFLAGS='-O3'
+    - ./configure --enable-tests CFLAGS='-O3'
     - make
     - sudo make install
   main_test_script:
@@ -26,8 +25,7 @@ mruby_freebsd_task:
     - unzip mruby-3.0.0.zip
   main_build_script:
     - ./autogen.sh
-    # FIXME: -Werror: unknown warning option '-Wno-cast-function-type'
-    - ./configure --disable-werror CFLAGS='-O3'
+    - ./configure CFLAGS='-O3'
     - make
     - sudo make install
   mruby_test_script:
@@ -47,8 +45,7 @@ ruby_freebsd_task:
     - sudo make install
   main_build_script:
     - ./autogen.sh
-    # FIXME: -Werror: unknown warning option '-Wno-cast-function-type'
-    - ./configure --disable-werror CFLAGS='-O3'
+    - ./configure CFLAGS='-O3'
     - make
     - sudo make install
   ruby_build_script:
@@ -70,8 +67,7 @@ rust_freebsd_task:
     - curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
   main_build_script:
     - ./autogen.sh
-    # FIXME: -Werror: unknown warning option '-Wno-cast-function-type'
-    - ./configure --disable-werror CFLAGS='-O3'
+    - ./configure CFLAGS='-O3'
     - make
     - sudo make install
   rust_test_script:
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 5113b1c..2a46c9c 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -13,12 +13,7 @@ jobs:
       matrix:
         # TODO: something is wrong with TCC, Multiboot 2 info tag struct size
         #cc: ['gcc', 'clang', 'tcc']
-        cc:
-          - cc: 'gcc'
-            werror: ''
-          - cc: 'clang'
-            # FIXME: -Werror: unknown warning option '-Wno-cast-function-type'
-            werror: '--disable-werror'
+        cc: ['gcc', 'clang']
         opt: ['', '-O0', '-O3']
     steps:
       - uses: actions/checkout@v2
@@ -27,7 +22,7 @@ jobs:
       - name: autogen
         run: ./autogen.sh
       - name: configure
-        run: ./configure --enable-tests ${{matrix.cc.werror}} CC='${{matrix.cc.cc}}' CFLAGS='${{matrix.opt}}'
+        run: ./configure --enable-tests CC='${{matrix.cc}}' CFLAGS='${{matrix.opt}}'
       - name: make
         run: make
       - name: check
diff --git a/Makefile.am b/Makefile.am
index 61f76cb..8a4239c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -5,7 +5,6 @@ AM_CFLAGS = \
 	-pedantic \
 	-Wall \
 	-Wextra \
-	-Wno-cast-function-type \
 	-I$(top_builddir)/include \
 	-I$(top_srcdir)/include
 
diff --git a/tests/multiboot2_header_print1.c b/tests/multiboot2_header_print1.c
index b13407c..33e20ba 100644
--- a/tests/multiboot2_header_print1.c
+++ b/tests/multiboot2_header_print1.c
@@ -5,10 +5,19 @@
 #include <kernaux/multiboot2.h>
 
 #include <assert.h>
+#include <stdarg.h>
 #include <stdio.h>
 
 #include "multiboot2_header_example1.h"
 
+static void my_printf(const char *format, ...)
+{
+    va_list va;
+    va_start(va, format);
+    vprintf(format, va);
+    va_end(va);
+}
+
 int main()
 {
     assert(KernAux_Multiboot2_Header_is_valid(
@@ -17,7 +26,7 @@ int main()
 
     KernAux_Multiboot2_Header_print(
         (struct KernAux_Multiboot2_Header*)&multiboot2_header_example1,
-        (void (*)(const char *format, ...))printf
+        my_printf
     );
 
     return 0;
diff --git a/tests/multiboot2_header_print2.c b/tests/multiboot2_header_print2.c
index 4c13b28..eff5bc8 100644
--- a/tests/multiboot2_header_print2.c
+++ b/tests/multiboot2_header_print2.c
@@ -5,10 +5,19 @@
 #include <kernaux/multiboot2.h>
 
 #include <assert.h>
+#include <stdarg.h>
 #include <stdio.h>
 
 #include "multiboot2_header_example2.h"
 
+static void my_printf(const char *format, ...)
+{
+    va_list va;
+    va_start(va, format);
+    vprintf(format, va);
+    va_end(va);
+}
+
 int main()
 {
     assert(KernAux_Multiboot2_Header_is_valid(
@@ -17,7 +26,7 @@ int main()
 
     KernAux_Multiboot2_Header_print(
         &multiboot2_header_example2.multiboot2_header,
-        (void (*)(const char *format, ...))printf
+        my_printf
     );
 
     return 0;
diff --git a/tests/multiboot2_info_print1.c b/tests/multiboot2_info_print1.c
index 6f71068..5e04422 100644
--- a/tests/multiboot2_info_print1.c
+++ b/tests/multiboot2_info_print1.c
@@ -5,10 +5,19 @@
 #include <kernaux/multiboot2.h>
 
 #include <assert.h>
+#include <stdarg.h>
 #include <stdio.h>
 
 #include "multiboot2_info_example1.h"
 
+static void my_printf(const char *format, ...)
+{
+    va_list va;
+    va_start(va, format);
+    vprintf(format, va);
+    va_end(va);
+}
+
 int main()
 {
     assert(KernAux_Multiboot2_Info_is_valid(
@@ -17,7 +26,7 @@ int main()
 
     KernAux_Multiboot2_Info_print(
         (struct KernAux_Multiboot2_Info*)multiboot2_info_example1,
-        (void (*)(const char *format, ...))printf
+        my_printf
     );
 
     return 0;
diff --git a/tests/multiboot2_info_print2.c b/tests/multiboot2_info_print2.c
index 0a744e8..705a079 100644
--- a/tests/multiboot2_info_print2.c
+++ b/tests/multiboot2_info_print2.c
@@ -5,10 +5,19 @@
 #include <kernaux/multiboot2.h>
 
 #include <assert.h>
+#include <stdarg.h>
 #include <stdio.h>
 
 #include "multiboot2_info_example2.h"
 
+static void my_printf(const char *format, ...)
+{
+    va_list va;
+    va_start(va, format);
+    vprintf(format, va);
+    va_end(va);
+}
+
 int main()
 {
     assert(KernAux_Multiboot2_Info_is_valid(
@@ -17,7 +26,7 @@ int main()
 
     KernAux_Multiboot2_Info_print(
         &multiboot2_info_example2.multiboot2_info,
-        (void (*)(const char *format, ...))printf
+        my_printf
     );
 
     return 0;