diff --git a/include/kernaux/stdlib.h b/include/kernaux/stdlib.h
index b134a09..0453c4a 100644
--- a/include/kernaux/stdlib.h
+++ b/include/kernaux/stdlib.h
@@ -1,6 +1,8 @@
 #ifndef KERNAUX_INCLUDED_STDLIB
 #define KERNAUX_INCLUDED_STDLIB 1
 
+#define KERNAUX_NULL ((void*)0)
+
 #define KERNAUX_FALSE ((kernaux_bool)0)
 #define KERNAUX_TRUE  ((kernaux_bool)1)
 
diff --git a/src/multiboot2/helpers.c b/src/multiboot2/helpers.c
index 4f4473a..562ec1e 100644
--- a/src/multiboot2/helpers.c
+++ b/src/multiboot2/helpers.c
@@ -9,7 +9,7 @@ const struct KernAux_Multiboot2_TagBase *KernAux_Multiboot2_first_tag_with_type(
 
     while ((void*)tag_base < (void*)multiboot2 + multiboot2->total_size) {
         if (!KernAux_Multiboot2_TagBase_is_valid(tag_base)) {
-            return 0;
+            return KERNAUX_NULL;
         }
 
         if (tag_base->type == tag_type) {
@@ -21,7 +21,7 @@ const struct KernAux_Multiboot2_TagBase *KernAux_Multiboot2_first_tag_with_type(
         );
     }
 
-    return 0;
+    return KERNAUX_NULL;
 }
 
 const struct KernAux_Multiboot2_TagBase *KernAux_Multiboot2_tag_with_type_after(
@@ -34,7 +34,7 @@ const struct KernAux_Multiboot2_TagBase *KernAux_Multiboot2_tag_with_type_after(
 
     while ((void*)tag_base < (void*)multiboot2 + multiboot2->total_size) {
         if (!KernAux_Multiboot2_TagBase_is_valid(tag_base)) {
-            return 0;
+            return KERNAUX_NULL;
         }
 
         if (tag_base->type == tag_type && tag_base > after_tag) {
@@ -46,7 +46,7 @@ const struct KernAux_Multiboot2_TagBase *KernAux_Multiboot2_tag_with_type_after(
         );
     }
 
-    return 0;
+    return KERNAUX_NULL;
 }
 
 const char *KernAux_Multiboot2_boot_cmd_line(
@@ -60,7 +60,7 @@ const char *KernAux_Multiboot2_boot_cmd_line(
         );
 
     if (!tag) {
-        return 0;
+        return KERNAUX_NULL;
     }
 
     return tag->cmdline;
diff --git a/src/multiboot2/is_valid.c b/src/multiboot2/is_valid.c
index d6f14dd..e078576 100644
--- a/src/multiboot2/is_valid.c
+++ b/src/multiboot2/is_valid.c
@@ -10,7 +10,7 @@ kernaux_bool KernAux_Multiboot2_is_valid(
     const struct KernAux_Multiboot2_TagBase *tag_base =
         (struct KernAux_Multiboot2_TagBase*)multiboot2->data;
 
-    const struct KernAux_Multiboot2_TagBase *none_tag_base = (void*)0;
+    const struct KernAux_Multiboot2_TagBase *none_tag_base = KERNAUX_NULL;
 
     while ((void*)tag_base < (void*)multiboot2 + multiboot2->total_size) {
         if (!KernAux_Multiboot2_TagBase_is_valid(tag_base)) {
@@ -18,7 +18,7 @@ kernaux_bool KernAux_Multiboot2_is_valid(
         }
 
         if (tag_base->type == KERNAUX_MULTIBOOT2_TAGTYPE_NONE &&
-            none_tag_base == 0
+            none_tag_base == KERNAUX_NULL
         ) {
             none_tag_base = tag_base;
         }
diff --git a/src/multiboot2/print.c b/src/multiboot2/print.c
index 5ac1309..986b33c 100644
--- a/src/multiboot2/print.c
+++ b/src/multiboot2/print.c
@@ -65,7 +65,7 @@ const char *KernAux_Multiboot2_TagType_to_str(
     case KERNAUX_MULTIBOOT2_TAGTYPE_IMAGE_LOAD_BASE_PHYS_ADDR:
         return "image load base phys addr";
     default:
-        return 0;
+        return KERNAUX_NULL;
     }
 }