diff --git a/AK/FuzzyMatch.cpp b/AK/FuzzyMatch.cpp
index 8a1e313895..f82db25af5 100644
--- a/AK/FuzzyMatch.cpp
+++ b/AK/FuzzyMatch.cpp
@@ -6,6 +6,7 @@
 
 #include <AK/CharacterTypes.h>
 #include <AK/FuzzyMatch.h>
+#include <string.h>
 
 namespace AK {
 
diff --git a/AK/JsonObjectSerializer.h b/AK/JsonObjectSerializer.h
index d18524843b..518856e66a 100644
--- a/AK/JsonObjectSerializer.h
+++ b/AK/JsonObjectSerializer.h
@@ -84,11 +84,11 @@ public:
         TRY(begin_item(key));
         if constexpr (IsLegacyBuilder<Builder>) {
             TRY(m_builder.try_append('"'));
-            TRY(m_builder.try_append_escaped_for_json({ value, strlen(value) }));
+            TRY(m_builder.try_append_escaped_for_json({ value, __builtin_strlen(value) }));
             TRY(m_builder.try_append('"'));
         } else {
             TRY(m_builder.append('"'));
-            TRY(m_builder.append_escaped_for_json({ value, strlen(value) }));
+            TRY(m_builder.append_escaped_for_json({ value, __builtin_strlen(value) }));
             TRY(m_builder.append('"'));
         }
         return {};
diff --git a/AK/PrintfImplementation.h b/AK/PrintfImplementation.h
index a1cd9243b0..7953ab074b 100644
--- a/AK/PrintfImplementation.h
+++ b/AK/PrintfImplementation.h
@@ -10,10 +10,10 @@
 #include <AK/StdLibExtras.h>
 #include <AK/Types.h>
 #include <stdarg.h>
-#include <wchar.h>
 
 #ifndef KERNEL
 #    include <math.h>
+#    include <wchar.h>
 #endif
 
 #ifdef AK_OS_SERENITY
diff --git a/AK/StringUtils.cpp b/AK/StringUtils.cpp
index 5640be9109..e544d5af77 100644
--- a/AK/StringUtils.cpp
+++ b/AK/StringUtils.cpp
@@ -14,9 +14,12 @@
 #include <AK/StringView.h>
 #include <AK/Vector.h>
 
-#ifndef KERNEL
+#ifdef KERNEL
+#    include <Kernel/StdLib.h>
+#else
 #    include <AK/DeprecatedString.h>
 #    include <AK/FloatingPointStringConversions.h>
+#    include <string.h>
 #endif
 
 namespace AK {
diff --git a/AK/Time.h b/AK/Time.h
index 0b13b4a48e..8a2382522a 100644
--- a/AK/Time.h
+++ b/AK/Time.h
@@ -11,12 +11,11 @@
 #include <AK/Platform.h>
 #include <AK/Types.h>
 
-// Kernel and Userspace pull in the definitions from different places.
-// Avoid trying to figure out which one.
-struct timeval;
-struct timespec;
-
-#if defined(AK_OS_WINDOWS)
+#if defined(AK_OS_SERENITY) && defined(KERNEL)
+#    include <Kernel/API/POSIX/sys/time.h>
+#    include <Kernel/API/POSIX/time.h>
+#else
+#    include <sys/time.h>
 #    include <time.h>
 #endif
 
diff --git a/AK/Traits.h b/AK/Traits.h
index cdcb9a85f7..901d97ed5d 100644
--- a/AK/Traits.h
+++ b/AK/Traits.h
@@ -11,7 +11,6 @@
 #include <AK/Forward.h>
 #include <AK/HashFunctions.h>
 #include <AK/StringHash.h>
-#include <string.h>
 
 namespace AK {
 
diff --git a/Kernel/Bus/USB/USBConfiguration.cpp b/Kernel/Bus/USB/USBConfiguration.cpp
index 93229d1e88..bf913f0006 100644
--- a/Kernel/Bus/USB/USBConfiguration.cpp
+++ b/Kernel/Bus/USB/USBConfiguration.cpp
@@ -9,6 +9,7 @@
 #include <Kernel/Bus/USB/USBConfiguration.h>
 #include <Kernel/Bus/USB/USBInterface.h>
 #include <Kernel/Bus/USB/USBRequest.h>
+#include <Kernel/StdLib.h>
 
 namespace Kernel::USB {
 
diff --git a/Kernel/Bus/USB/USBTransfer.cpp b/Kernel/Bus/USB/USBTransfer.cpp
index ada524d4f0..528df1ae30 100644
--- a/Kernel/Bus/USB/USBTransfer.cpp
+++ b/Kernel/Bus/USB/USBTransfer.cpp
@@ -6,6 +6,7 @@
 
 #include <Kernel/Bus/USB/USBTransfer.h>
 #include <Kernel/Memory/MemoryManager.h>
+#include <Kernel/StdLib.h>
 
 namespace Kernel::USB {
 
diff --git a/Kernel/FileSystem/Ext2FS/Inode.cpp b/Kernel/FileSystem/Ext2FS/Inode.cpp
index 9ac62cb7d6..29436f1821 100644
--- a/Kernel/FileSystem/Ext2FS/Inode.cpp
+++ b/Kernel/FileSystem/Ext2FS/Inode.cpp
@@ -992,11 +992,11 @@ ErrorOr<void> Ext2FSInode::update_timestamps(Optional<Time> atime, Optional<Time
     MutexLocker locker(m_inode_lock);
     if (fs().is_readonly())
         return EROFS;
-    if (atime.value_or({}).to_timespec().tv_sec > INT32_MAX)
+    if (atime.value_or({}).to_timespec().tv_sec > NumericLimits<i32>::max())
         return EINVAL;
-    if (ctime.value_or({}).to_timespec().tv_sec > INT32_MAX)
+    if (ctime.value_or({}).to_timespec().tv_sec > NumericLimits<i32>::max())
         return EINVAL;
-    if (mtime.value_or({}).to_timespec().tv_sec > INT32_MAX)
+    if (mtime.value_or({}).to_timespec().tv_sec > NumericLimits<i32>::max())
         return EINVAL;
     if (atime.has_value())
         m_raw_inode.i_atime = atime.value().to_timespec().tv_sec;
diff --git a/Kernel/KBuffer.h b/Kernel/KBuffer.h
index a3bf599820..77a1729b8a 100644
--- a/Kernel/KBuffer.h
+++ b/Kernel/KBuffer.h
@@ -18,6 +18,7 @@
 #include <AK/Assertions.h>
 #include <AK/StringView.h>
 #include <Kernel/Memory/MemoryManager.h>
+#include <Kernel/StdLib.h> // For memcpy. FIXME: Make memcpy less expensive to access a declaration of in the Kernel.
 
 namespace Kernel {
 
diff --git a/Kernel/StdLib.h b/Kernel/StdLib.h
index d45d33872e..b420e0dc44 100644
--- a/Kernel/StdLib.h
+++ b/Kernel/StdLib.h
@@ -51,6 +51,8 @@ void const* memmem(void const* haystack, size_t, void const* needle, size_t);
 [[nodiscard]] inline u16 htons(u16 w) { return (w & 0xff) << 8 | ((w >> 8) & 0xff); }
 }
 
+#define offsetof(type, member) __builtin_offsetof(type, member)
+
 template<typename T>
 [[nodiscard]] inline ErrorOr<void> copy_from_user(T* dest, T const* src)
 {
diff --git a/Userland/Libraries/LibEDID/EDID.cpp b/Userland/Libraries/LibEDID/EDID.cpp
index a3f930b2fa..d50d896426 100644
--- a/Userland/Libraries/LibEDID/EDID.cpp
+++ b/Userland/Libraries/LibEDID/EDID.cpp
@@ -10,7 +10,9 @@
 #include <AK/Try.h>
 #include <LibEDID/EDID.h>
 
-#ifndef KERNEL
+#ifdef KERNEL
+#    include <Kernel/StdLib.h>
+#else
 #    include <AK/ScopeGuard.h>
 #    include <Kernel/API/Graphics.h>
 #    include <fcntl.h>
diff --git a/Userland/Libraries/LibELF/Image.cpp b/Userland/Libraries/LibELF/Image.cpp
index cc73528f61..bd66b3f165 100644
--- a/Userland/Libraries/LibELF/Image.cpp
+++ b/Userland/Libraries/LibELF/Image.cpp
@@ -14,7 +14,12 @@
 #include <Kernel/API/serenity_limits.h>
 #include <LibELF/Image.h>
 #include <LibELF/Validation.h>
-#include <limits.h>
+
+#ifdef KERNEL
+#    include <Kernel/StdLib.h>
+#else
+#    include <string.h>
+#endif
 
 namespace ELF {
 
diff --git a/Userland/Libraries/LibELF/Validation.cpp b/Userland/Libraries/LibELF/Validation.cpp
index 8005b78a3c..be76b0b3df 100644
--- a/Userland/Libraries/LibELF/Validation.cpp
+++ b/Userland/Libraries/LibELF/Validation.cpp
@@ -10,8 +10,11 @@
 #include <Kernel/API/serenity_limits.h>
 #include <LibC/elf.h>
 #include <LibELF/Validation.h>
-#include <limits.h>
-#include <pthread.h>
+
+#ifndef KERNEL
+#    include <limits.h>
+#    include <pthread.h>
+#endif
 
 namespace ELF {