diff --git a/kernel/include/errno.h b/kernel/include/errno.h
index c02a1dcd..64cb4364 100644
--- a/kernel/include/errno.h
+++ b/kernel/include/errno.h
@@ -2,4 +2,5 @@
 
 #define EPERM 1
 #define ENOMEM 12
-#define EINVAL 22
\ No newline at end of file
+#define EINVAL 22
+#define ENOSYS 38
\ No newline at end of file
diff --git a/kernel/src/sys/Syscall.cpp b/kernel/src/sys/Syscall.cpp
index 1f11e5b4..26785759 100644
--- a/kernel/src/sys/Syscall.cpp
+++ b/kernel/src/sys/Syscall.cpp
@@ -1,4 +1,5 @@
 #include "sys/Syscall.h"
+#include "errno.h"
 #include "io/Serial.h"
 #include "thread/Scheduler.h"
 
@@ -25,6 +26,6 @@ void Syscall::entry(Context* context)
     case SYS_gettid: sys_gettid(context); break;
     case SYS_mmap: sys_mmap(context, (void*)context->rdi, context->rsi, (int)context->rdx); break;
     case SYS_munmap: sys_munmap(context, (void*)context->rdi, context->rsi); break;
-    default: context->rax = -1; break;
+    default: context->rax = -ENOSYS; break;
     }
 }
\ No newline at end of file
diff --git a/libs/libc/include/errno.h b/libs/libc/include/errno.h
index 1caae45e..27deecbf 100644
--- a/libs/libc/include/errno.h
+++ b/libs/libc/include/errno.h
@@ -6,5 +6,6 @@ extern int errno;
 #define EPERM 1
 #define ENOMEM 12
 #define EINVAL 22
+#define ENOSYS 38
 
 #endif
\ No newline at end of file
diff --git a/libs/libc/src/string.cpp b/libs/libc/src/string.cpp
index b9d32192..c99ef0ad 100644
--- a/libs/libc/src/string.cpp
+++ b/libs/libc/src/string.cpp
@@ -120,6 +120,7 @@ extern "C"
         case EPERM: return "Operation not permitted";
         case EINVAL: return "Invalid argument";
         case ENOMEM: return "Out of memory";
+        case ENOSYS: return "Function not implemented";
         default: return 0;
         }
     }
diff --git a/libs/libc/src/unistd.cpp b/libs/libc/src/unistd.cpp
index 25ef02cb..84ae01d3 100644
--- a/libs/libc/src/unistd.cpp
+++ b/libs/libc/src/unistd.cpp
@@ -60,7 +60,7 @@ extern "C"
             result = __luna_syscall5(number, arg0, arg1, arg2, arg3, arg4);
             break;
         }
-        default: result = -1; break;
+        default: result = -ENOSYS; break;
         }
         va_end(ap);
         if (number == SYS_mmap) { _RETURN_WITH_MEMORY_ERRNO(result, long int); }