diff --git a/apps/src/memeater.c b/apps/src/memeater.c
index 875d319b..8e683637 100644
--- a/apps/src/memeater.c
+++ b/apps/src/memeater.c
@@ -1,3 +1,4 @@
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -13,5 +14,6 @@ int main()
         printf("Allocating 4 MB of memory... %lx\n", (unsigned long)allocated);
         sleep(1);
     } while ((allocated = malloc(CHUNK)));
-    printf("Out of memory.\n");
+    printf("Out of memory. (errno=%d)\n", errno);
+    printf("Press any key to restart.\n");
 }
\ No newline at end of file
diff --git a/kernel/include/errno.h b/kernel/include/errno.h
new file mode 100644
index 00000000..c02a1dcd
--- /dev/null
+++ b/kernel/include/errno.h
@@ -0,0 +1,5 @@
+#pragma once
+
+#define EPERM 1
+#define ENOMEM 12
+#define EINVAL 22
\ No newline at end of file
diff --git a/kernel/src/sys/mem.cpp b/kernel/src/sys/mem.cpp
index f87843c6..148bb964 100644
--- a/kernel/src/sys/mem.cpp
+++ b/kernel/src/sys/mem.cpp
@@ -1,17 +1,20 @@
 #define MODULE "mem"
 
+#include "errno.h"
 #include "interrupts/Context.h"
 #include "log/Log.h"
 #include "memory/MemoryManager.h"
 #include "memory/VMM.h"
 #include <stddef.h>
 
+#define MAP_FAIL(errno) 0xffffffffffffff00 | (unsigned char)(errno)
+
 void sys_mmap(Context* context, void* address, size_t size, int flags)
 {
     if (size < 4096)
     {
         kdbgln("sys_mmap: size too small");
-        context->rax = 0;
+        context->rax = MAP_FAIL(EINVAL);
         return;
     }
     int real_flags = MAP_USER;
@@ -23,7 +26,7 @@ void sys_mmap(Context* context, void* address, size_t size, int flags)
         if (kernelVMM.getPhysical((uint64_t)address) != (uint64_t)-1) // Address is already used.
         {
             kdbgln("attempt to mmap an already mapped address");
-            context->rax = 0;
+            context->rax = MAP_FAIL(ENOMEM);
             return;
         }
         uint64_t offset = (uint64_t)address % 4096;
@@ -37,7 +40,7 @@ void sys_mmap(Context* context, void* address, size_t size, int flags)
         else
         {
             kdbgln("mmap failed");
-            context->rax = 0;
+            context->rax = MAP_FAIL(ENOMEM);
             return;
         }
     }
@@ -52,7 +55,7 @@ void sys_mmap(Context* context, void* address, size_t size, int flags)
     else
     {
         kdbgln("mmap failed");
-        context->rax = 0;
+        context->rax = MAP_FAIL(ENOMEM);
         return;
     }
 }
@@ -60,17 +63,23 @@ void sys_mmap(Context* context, void* address, size_t size, int flags)
 void sys_munmap(Context* context, void* address, size_t size)
 {
     kdbgln("sys_munmap: attempting to unmap %lx", (uint64_t)address);
+    if (size < 4096)
+    {
+        kdbgln("munmap failed: size is too small");
+        context->rax = -EINVAL;
+        return;
+    }
     if (!address)
     {
         kdbgln("munmap failed: attempted to unmap page 0");
-        context->rax = -1;
+        context->rax = -EINVAL;
         return;
     }
     uint64_t flags = kernelVMM.getFlags((uint64_t)address);
     if (!(flags & MAP_USER))
     {
         kdbgln("munmap failed: attempted to unmap a kernel page");
-        context->rax = -1;
+        context->rax = -EINVAL;
         return;
     }
     uint64_t offset = (uint64_t)address % 4096;
diff --git a/kernel/src/sys/paint.cpp b/kernel/src/sys/paint.cpp
index 9a56de2a..daece6cd 100644
--- a/kernel/src/sys/paint.cpp
+++ b/kernel/src/sys/paint.cpp
@@ -1,4 +1,5 @@
 #include "bootboot.h"
+#include "errno.h"
 #include "interrupts/Context.h"
 #include "render/Framebuffer.h"
 #include <stdint.h>
@@ -9,12 +10,12 @@ void sys_paint(Context* context, uint64_t x, uint64_t y, uint64_t w, uint64_t h,
 {
     if ((x + w) > bootboot.fb_width)
     {
-        context->rax = -1;
+        context->rax = -EINVAL;
         return;
     }
     if ((y + h) > bootboot.fb_height)
     {
-        context->rax = -1;
+        context->rax = -EINVAL;
         return;
     }
 
diff --git a/kernel/src/sys/version.cpp b/kernel/src/sys/version.cpp
index 62a53c1c..f8bd51a3 100644
--- a/kernel/src/sys/version.cpp
+++ b/kernel/src/sys/version.cpp
@@ -1,8 +1,19 @@
 #include "config.h"
+#include "errno.h"
 #include "interrupts/Context.h"
 #include "std/stdio.h"
 
 void sys_getversion(Context* context, char* buffer, size_t max)
 {
+    if (!max)
+    {
+        context->rax = -EINVAL;
+        return;
+    }
+    if (!buffer)
+    {
+        context->rax = -EINVAL;
+        return;
+    }
     context->rax = snprintf(buffer, max, "moon %s", moon_version());
 }
\ No newline at end of file
diff --git a/libs/libc/include/bits/error.h b/libs/libc/include/bits/error.h
new file mode 100644
index 00000000..607695d8
--- /dev/null
+++ b/libs/libc/include/bits/error.h
@@ -0,0 +1,26 @@
+#ifndef _BITS_ERROR_H
+#define _BITS_ERROR_H
+
+#include <errno.h>
+
+#define _RETURN_WITH_ERRNO(rc, type)                                                                                   \
+    do {                                                                                                               \
+        if (rc < 0)                                                                                                    \
+        {                                                                                                              \
+            errno = (int)rc;                                                                                           \
+            return -1;                                                                                                 \
+        }                                                                                                              \
+        return (type)rc;                                                                                               \
+    } while (0)
+
+#define _RETURN_WITH_MEMORY_ERRNO(rc, type)                                                                            \
+    do {                                                                                                               \
+        if ((unsigned long int)rc > 0xffffffffffffff00)                                                                \
+        {                                                                                                              \
+            errno = (int)((rc)&0xff);                                                                                  \
+            return (type)-1;                                                                                           \
+        }                                                                                                              \
+        return (type)rc;                                                                                               \
+    } while (0)
+
+#endif
\ No newline at end of file
diff --git a/libs/libc/include/bits/macros.h b/libs/libc/include/bits/macros.h
index 3bc212ec..16ede7b4 100644
--- a/libs/libc/include/bits/macros.h
+++ b/libs/libc/include/bits/macros.h
@@ -1,5 +1,5 @@
-#ifndef __BITS_MACROS_H
-#define __BITS_MACROS_H
+#ifndef _BITS_MACROS_H
+#define _BITS_MACROS_H
 
 #define noreturn __attribute__((noreturn))
 #define align(n) __attribute__((aligned(n)))
diff --git a/libs/libc/include/errno.h b/libs/libc/include/errno.h
index e69de29b..1caae45e 100644
--- a/libs/libc/include/errno.h
+++ b/libs/libc/include/errno.h
@@ -0,0 +1,10 @@
+#ifndef _ERRNO_H
+#define _ERRNO_H
+
+extern int errno;
+
+#define EPERM 1
+#define ENOMEM 12
+#define EINVAL 22
+
+#endif
\ No newline at end of file
diff --git a/libs/libc/include/sys/mman.h b/libs/libc/include/sys/mman.h
new file mode 100644
index 00000000..3843a85d
--- /dev/null
+++ b/libs/libc/include/sys/mman.h
@@ -0,0 +1,22 @@
+#ifndef _SYS_MMAN_H
+#define _SYS_MMAN_H
+
+#include <stddef.h>
+
+typedef unsigned long off_t;
+
+#define MAP_FAILED (void*)-1
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+    void* mmap(void*, size_t, int, int, int, off_t);
+    int munmap(void* addr, size_t len);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
\ No newline at end of file
diff --git a/libs/libc/src/bits/bindings.c b/libs/libc/src/bits/bindings.c
index f8601d34..75b85898 100644
--- a/libs/libc/src/bits/bindings.c
+++ b/libs/libc/src/bits/bindings.c
@@ -1,6 +1,5 @@
 #include <stddef.h>
-#include <sys/syscall.h>
-#include <unistd.h>
+#include <sys/mman.h>
 
 int liballoc_lock()
 {
@@ -14,14 +13,12 @@ int liballoc_unlock()
 
 void* liballoc_alloc(size_t size)
 {
-    unsigned long int result = (unsigned long int)syscall(SYS_mmap, NULL, size * 4096, 1);
+    void* result = mmap(NULL, size * 4096, 0, 1, 0, 0);
+    if (result == MAP_FAILED) return 0;
     return (void*)result;
 }
 
 int liballoc_free(void* address, size_t size)
 {
-    int result = (int)syscall(SYS_munmap, address, size * 4096);
-    if (result < 0) return 1;
-    else
-        return 0;
+    return munmap(address, size * 4096);
 }
\ No newline at end of file
diff --git a/libs/libc/src/errno.cpp b/libs/libc/src/errno.cpp
new file mode 100644
index 00000000..434ba1ab
--- /dev/null
+++ b/libs/libc/src/errno.cpp
@@ -0,0 +1,3 @@
+#include <errno.h>
+
+int errno;
\ No newline at end of file
diff --git a/libs/libc/src/luna.cpp b/libs/libc/src/luna.cpp
index abef73a9..eee9f2ae 100644
--- a/libs/libc/src/luna.cpp
+++ b/libs/libc/src/luna.cpp
@@ -1,4 +1,5 @@
 #include <luna.h>
+#include <stdlib.h>
 #include <string.h>
 #include <sys/syscall.h>
 #include <unistd.h>
@@ -20,7 +21,6 @@ extern "C"
     noreturn void __luna_abort(const char* message)
     {
         syscall(SYS_write, message, strlen(message));
-        syscall(SYS_exit);
-        __builtin_unreachable();
+        abort();
     }
 }
\ No newline at end of file
diff --git a/libs/libc/src/stdio.cpp b/libs/libc/src/stdio.cpp
index d2da8940..eecf7621 100644
--- a/libs/libc/src/stdio.cpp
+++ b/libs/libc/src/stdio.cpp
@@ -50,6 +50,7 @@ extern "C"
     int puts(const char* s)
     {
         long nwritten = syscall(SYS_write, s, strlen(s));
+        if (nwritten < 0) return -1;
         nwritten += syscall(SYS_write, "\n", 1);
         return (int)nwritten;
     }
diff --git a/libs/libc/src/sys/mman.cpp b/libs/libc/src/sys/mman.cpp
new file mode 100644
index 00000000..7b2a747f
--- /dev/null
+++ b/libs/libc/src/sys/mman.cpp
@@ -0,0 +1,17 @@
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+extern "C"
+{
+    // FIXME: Implement a POSIX-compliant mmap.
+    void* mmap(void* addr, size_t len, int, int flags, int, off_t)
+    {
+        return (void*)syscall(SYS_mmap, addr, len, flags);
+    }
+
+    int munmap(void* addr, size_t len)
+    {
+        return (int)syscall(SYS_munmap, addr, len);
+    }
+}
\ No newline at end of file
diff --git a/libs/libc/src/unistd.cpp b/libs/libc/src/unistd.cpp
index 2e3e6593..25ef02cb 100644
--- a/libs/libc/src/unistd.cpp
+++ b/libs/libc/src/unistd.cpp
@@ -1,3 +1,4 @@
+#include <bits/error.h>
 #include <luna.h>
 #include <luna/syscall.h>
 #include <stdarg.h>
@@ -62,7 +63,8 @@ extern "C"
         default: result = -1; break;
         }
         va_end(ap);
-        return result;
+        if (number == SYS_mmap) { _RETURN_WITH_MEMORY_ERRNO(result, long int); }
+        else { _RETURN_WITH_ERRNO(result, long); }
     }
 
     unsigned int sleep(unsigned int seconds)