diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 42ef4ed..e2b03ba 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -7,7 +7,7 @@ on:
     branches: [master]
 
 jobs:
-  test_deny_warnings:
+  nowarn_assert_defopt:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
@@ -20,7 +20,72 @@ jobs:
       - name: check
         run: make check
 
-  test_allow_warnings:
+  nowarn_assert_noopt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: autogen
+        run: ./autogen.sh
+      - name: configure
+        run: ./configure --enable-assert --disable-multiboot2 CFLAGS='-O0 -Werror'
+      - name: make
+        run: make
+      - name: check
+        run: make check
+
+  nowarn_assert_maxopt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: autogen
+        run: ./autogen.sh
+      - name: configure
+        run: ./configure --disable-assert --disable-multiboot2 CFLAGS='-O3 -Werror'
+      - name: make
+        run: make
+      - name: check
+        run: make check
+
+  nowarn_noassert_defopt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: autogen
+        run: ./autogen.sh
+      - name: configure
+        run: ./configure --disable-assert --disable-multiboot2 CFLAGS='-Werror'
+      - name: make
+        run: make
+      - name: check
+        run: make check
+
+  nowarn_noassert_noopt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: autogen
+        run: ./autogen.sh
+      - name: configure
+        run: ./configure --disable-assert --disable-multiboot2 CFLAGS='-O0 -Werror'
+      - name: make
+        run: make
+      - name: check
+        run: make check
+
+  nowarn_noassert_maxopt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: autogen
+        run: ./autogen.sh
+      - name: configure
+        run: ./configure --disable-assert --disable-multiboot2 CFLAGS='-O3 -Werror'
+      - name: make
+        run: make
+      - name: check
+        run: make check
+
+  warn_assert_defopt:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
@@ -32,3 +97,68 @@ jobs:
         run: make
       - name: check
         run: make check
+
+  warn_assert_noopt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: autogen
+        run: ./autogen.sh
+      - name: configure
+        run: ./configure --enable-assert CFLAGS='-O0'
+      - name: make
+        run: make
+      - name: check
+        run: make check
+
+  warn_assert_maxopt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: autogen
+        run: ./autogen.sh
+      - name: configure
+        run: ./configure --disable-assert CFLAGS='-O3'
+      - name: make
+        run: make
+      - name: check
+        run: make check
+
+  warn_noassert_defopt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: autogen
+        run: ./autogen.sh
+      - name: configure
+        run: ./configure --disable-assert
+      - name: make
+        run: make
+      - name: check
+        run: make check
+
+  warn_noassert_noopt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: autogen
+        run: ./autogen.sh
+      - name: configure
+        run: ./configure --disable-assert CFLAGS='-O0'
+      - name: make
+        run: make
+      - name: check
+        run: make check
+
+  warn_noassert_maxopt:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: autogen
+        run: ./autogen.sh
+      - name: configure
+        run: ./configure --disable-assert CFLAGS='-O3'
+      - name: make
+        run: make
+      - name: check
+        run: make check
diff --git a/.gitignore b/.gitignore
index a49f5c5..0482685 100644
--- a/.gitignore
+++ b/.gitignore
@@ -49,6 +49,7 @@
 /tests/test_multiboot2_print
 /tests/test_multiboot2_validation
 /tests/test_pfa
+/tests/test_pfa_assert
 /tests/test_printf
 /tests/test_stdlib
 /tests/test_units_human
diff --git a/Makefile.am b/Makefile.am
index bd4e188..f28d85e 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -68,7 +68,8 @@ if ENABLE_PFA
 libkernaux_a_SOURCES += src/pfa.c
 TESTS += \
 	examples/pfa \
-	tests/test_pfa
+	tests/test_pfa \
+	tests/test_pfa_assert
 endif
 
 if ENABLE_UNITS
@@ -134,6 +135,10 @@ tests_test_pfa_SOURCES = \
 	$(libkernaux_a_SOURCES) \
 	tests/test_pfa.c
 
+tests_test_pfa_assert_SOURCES = \
+	$(libkernaux_a_SOURCES) \
+	tests/test_pfa_assert.c
+
 tests_test_printf_SOURCES = \
 	$(libkernaux_a_SOURCES) \
 	tests/test_printf.c
diff --git a/include/kernaux/pfa.h b/include/kernaux/pfa.h
index 1bf46c2..e419967 100644
--- a/include/kernaux/pfa.h
+++ b/include/kernaux/pfa.h
@@ -18,23 +18,15 @@ struct KernAux_PFA {
     unsigned char flags[KERNAUX_PFA_FLAGS_SIZE];
 };
 
-void KernAux_PFA_initialize(KernAux_PFA pfa)
-__attribute__((nonnull));
+void KernAux_PFA_initialize(KernAux_PFA pfa);
 
-bool KernAux_PFA_is_available(KernAux_PFA pfa, size_t page_addr)
-__attribute__((nonnull));
+bool KernAux_PFA_is_available(KernAux_PFA pfa, size_t page_addr);
 
-void KernAux_PFA_mark_available(KernAux_PFA pfa, size_t start, size_t end)
-__attribute__((nonnull));
+void KernAux_PFA_mark_available(KernAux_PFA pfa, size_t start, size_t end);
+void KernAux_PFA_mark_unavailable(KernAux_PFA pfa, size_t start, size_t end);
 
-void KernAux_PFA_mark_unavailable(KernAux_PFA pfa, size_t start, size_t end)
-__attribute__((nonnull));
-
-size_t KernAux_PFA_alloc_pages(KernAux_PFA pfa, size_t mem_size)
-__attribute__((nonnull));
-
-void KernAux_PFA_free_pages(KernAux_PFA pfa, size_t page_addr, size_t mem_size)
-__attribute__((nonnull));
+size_t KernAux_PFA_alloc_pages(KernAux_PFA pfa, size_t mem_size);
+void KernAux_PFA_free_pages(KernAux_PFA pfa, size_t page_addr, size_t mem_size);
 
 #ifdef __cplusplus
 }
diff --git a/src/pfa.c b/src/pfa.c
index 70d6a41..5e048ef 100644
--- a/src/pfa.c
+++ b/src/pfa.c
@@ -36,18 +36,17 @@ static void KernAux_PFA_mark(
     bool status,
     size_t start,
     size_t end
-)
-__attribute__((nonnull));
+);
 
 void KernAux_PFA_initialize(const KernAux_PFA pfa)
 {
-    assert(pfa);
+    assert_return(pfa);
     kernaux_memset(pfa->flags, 0, sizeof(pfa->flags));
 }
 
 bool KernAux_PFA_is_available(const KernAux_PFA pfa, const size_t page_addr)
 {
-    assert(pfa);
+    assert_retval(pfa, false);
     assert_retval(page_addr % KERNAUX_PFA_PAGE_SIZE == 0, false);
 
     return GET_FLAG_FROM_ADDR(pfa, page_addr);
@@ -75,7 +74,7 @@ void KernAux_PFA_mark(
     size_t start,
     size_t end
 ) {
-    assert(pfa);
+    assert_return(pfa);
     assert_return(start < end);
 
     const size_t start_rem = start % KERNAUX_PFA_PAGE_SIZE;
@@ -103,7 +102,7 @@ void KernAux_PFA_mark(
 
 size_t KernAux_PFA_alloc_pages(const KernAux_PFA pfa, size_t mem_size)
 {
-    assert(pfa);
+    assert_retval(pfa, 0);
 
     const size_t mem_rem = mem_size % KERNAUX_PFA_PAGE_SIZE;
 
@@ -142,7 +141,7 @@ void KernAux_PFA_free_pages(
     const size_t page_addr,
     size_t mem_size
 ) {
-    assert(pfa);
+    assert_return(pfa);
     assert_return(page_addr % KERNAUX_PFA_PAGE_SIZE == 0);
 
     const size_t mem_rem = mem_size % KERNAUX_PFA_PAGE_SIZE;
diff --git a/tests/test_pfa_assert.c b/tests/test_pfa_assert.c
new file mode 100644
index 0000000..63c1766
--- /dev/null
+++ b/tests/test_pfa_assert.c
@@ -0,0 +1,73 @@
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <kernaux/assert.h>
+#include <kernaux/pfa.h>
+
+#include <assert.h>
+#include <stddef.h>
+
+static unsigned int count = 0;
+
+static void test();
+
+static void assert_cb(
+    __attribute__((unused))
+    const char *const file,
+    __attribute__((unused))
+    const int line,
+    __attribute__((unused))
+    const char *const str
+) {
+    ++count;
+}
+
+int main()
+{
+    kernaux_assert_cb = NULL;
+    test();
+
+#ifdef ENABLE_ASSERT
+    kernaux_assert_cb = assert_cb;
+    test();
+#endif
+
+    return 0;
+}
+
+void test()
+{
+    struct KernAux_PFA pfa;
+    KernAux_PFA_initialize(&pfa);
+
+    KernAux_PFA_initialize(NULL);
+    if (kernaux_assert_cb) assert(count == 1);
+
+    assert(!KernAux_PFA_is_available(NULL, KERNAUX_PFA_PAGE_SIZE));
+    if (kernaux_assert_cb) assert(count == 2);
+
+    assert(!KernAux_PFA_is_available(&pfa, 123));
+    if (kernaux_assert_cb) assert(count == 3);
+
+    KernAux_PFA_mark_available(NULL, 0, KERNAUX_PFA_PAGE_SIZE);
+    if (kernaux_assert_cb) assert(count == 4);
+
+    KernAux_PFA_mark_available(&pfa, KERNAUX_PFA_PAGE_SIZE, 0);
+    if (kernaux_assert_cb) assert(count == 5);
+
+    KernAux_PFA_mark_unavailable(NULL, 0, KERNAUX_PFA_PAGE_SIZE);
+    if (kernaux_assert_cb) assert(count == 6);
+
+    KernAux_PFA_mark_unavailable(&pfa, KERNAUX_PFA_PAGE_SIZE, 0);
+    if (kernaux_assert_cb) assert(count == 7);
+
+    assert(KernAux_PFA_alloc_pages(NULL, KERNAUX_PFA_PAGE_SIZE) == 0);
+    if (kernaux_assert_cb) assert(count == 8);
+
+    KernAux_PFA_free_pages(NULL, KERNAUX_PFA_PAGE_SIZE, KERNAUX_PFA_PAGE_SIZE);
+    if (kernaux_assert_cb) assert(count == 9);
+
+    KernAux_PFA_free_pages(&pfa, 123, KERNAUX_PFA_PAGE_SIZE);
+    if (kernaux_assert_cb) assert(count == 10);
+}