diff --git a/include/kernaux/ntoa.h b/include/kernaux/ntoa.h
index adb073f..fd9dc71 100644
--- a/include/kernaux/ntoa.h
+++ b/include/kernaux/ntoa.h
@@ -7,11 +7,12 @@ extern "C" {
 
 #include <stdint.h>
 
-// TODO: define
-#define KERNAUX_UTOA_BUFFER_SIZE (0/0)
+// "1111111111111111111111111111111111111111111111111111111111111111"
+#define KERNAUX_UTOA_BUFFER_SIZE 65
 
-// TODO: define
-#define KERNAUX_ITOA_BUFFER_SIZE (0/0)
+// "111111111111111111111111111111111111111111111111111111111111111"
+// "-1000000000000000000000000000000000000000000000000000000000000000"
+#define KERNAUX_ITOA_BUFFER_SIZE 66
 
 // "18446744073709551615"
 #define KERNAUX_UTOA10_BUFFER_SIZE 21
diff --git a/tests/test_ntoa.c b/tests/test_ntoa.c
index 0845589..633ebcb 100644
--- a/tests/test_ntoa.c
+++ b/tests/test_ntoa.c
@@ -365,8 +365,7 @@ static const struct {
 int main()
 {
     {
-        // TODO: replace 1000 with KERNAUX_UTOA_BUFFER_SIZE
-        char buffer[1000];
+        char buffer[KERNAUX_UTOA_BUFFER_SIZE];
 
         for (
             size_t index = 0;
@@ -389,8 +388,7 @@ int main()
     }
 
     {
-        // TODO: replace 1000 with KERNAUX_ITOA_BUFFER_SIZE
-        char buffer[1000];
+        char buffer[KERNAUX_ITOA_BUFFER_SIZE];
 
         for (
             size_t index = 0;