diff --git a/src/multiboot2/header_is_valid.c b/src/multiboot2/header_is_valid.c
index 8cc2bf4..fb8cc84 100644
--- a/src/multiboot2/header_is_valid.c
+++ b/src/multiboot2/header_is_valid.c
@@ -5,12 +5,56 @@
 #include <kernaux/multiboot2.h>
 
 #include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
 
 bool KernAux_Multiboot2_Header_is_valid(
     const struct KernAux_Multiboot2_Header *const multiboot2_header
 ) {
-    // TODO: write this
-    return false;
+    if (multiboot2_header->total_size <
+        sizeof(struct KernAux_Multiboot2_Header) +
+        sizeof(struct KernAux_Multiboot2_HTag_None))
+    {
+        return false;
+    }
+
+    const struct KernAux_Multiboot2_HTagBase *tag_base =
+        (struct KernAux_Multiboot2_HTagBase*)
+        KERNAUX_MULTIBOOT2_DATA(multiboot2_header);
+
+    const struct KernAux_Multiboot2_HTagBase *none_tag_base = NULL;
+
+    while (tag_base <
+           (struct KernAux_Multiboot2_HTagBase*)
+           ((uint8_t*)multiboot2_header + multiboot2_header->total_size))
+    {
+        if (!KernAux_Multiboot2_HTagBase_is_valid(tag_base)) return false;
+
+        if (tag_base->type == KERNAUX_MULTIBOOT2_HTAG_NONE &&
+            none_tag_base == NULL
+        ) {
+            none_tag_base = tag_base;
+        }
+
+        tag_base = KERNAUX_MULTIBOOT2_HTAG_NEXT(tag_base);
+    }
+
+    if (tag_base !=
+        (struct KernAux_Multiboot2_HTagBase*)
+        ((uint8_t*)multiboot2_header + multiboot2_header->total_size))
+    {
+        return false;
+    }
+
+    if (none_tag_base !=
+        (struct KernAux_Multiboot2_HTagBase*)
+        ((uint8_t*)tag_base -
+         sizeof(struct KernAux_Multiboot2_HTag_None)))
+    {
+        return false;
+    }
+
+    return true;
 }
 
 bool KernAux_Multiboot2_HTagBase_is_valid(
diff --git a/src/multiboot2/info_is_valid.c b/src/multiboot2/info_is_valid.c
index 7e35057..64be3bd 100644
--- a/src/multiboot2/info_is_valid.c
+++ b/src/multiboot2/info_is_valid.c
@@ -6,11 +6,17 @@
 
 #include <stdbool.h>
 #include <stddef.h>
+#include <stdint.h>
 
 bool KernAux_Multiboot2_Info_is_valid(
     const struct KernAux_Multiboot2_Info *const multiboot2_info
 ) {
-    if (multiboot2_info->total_size <= 8) return false;
+    if (multiboot2_info->total_size <
+        sizeof(struct KernAux_Multiboot2_Info) +
+        sizeof(struct KernAux_Multiboot2_ITag_None))
+    {
+        return false;
+    }
 
     const struct KernAux_Multiboot2_ITagBase *tag_base =
         (struct KernAux_Multiboot2_ITagBase*)
@@ -20,7 +26,7 @@ bool KernAux_Multiboot2_Info_is_valid(
 
     while (tag_base <
            (struct KernAux_Multiboot2_ITagBase*)
-           ((unsigned char*)multiboot2_info + multiboot2_info->total_size))
+           ((uint8_t*)multiboot2_info + multiboot2_info->total_size))
     {
         if (!KernAux_Multiboot2_ITagBase_is_valid(tag_base)) return false;
 
@@ -35,14 +41,14 @@ bool KernAux_Multiboot2_Info_is_valid(
 
     if (tag_base !=
         (struct KernAux_Multiboot2_ITagBase*)
-        ((unsigned char*)multiboot2_info + multiboot2_info->total_size))
+        ((uint8_t*)multiboot2_info + multiboot2_info->total_size))
     {
         return false;
     }
 
     if (none_tag_base !=
         (struct KernAux_Multiboot2_ITagBase*)
-        ((unsigned char*)tag_base -
+        ((uint8_t*)tag_base -
          sizeof(struct KernAux_Multiboot2_ITag_None)))
     {
         return false;