diff --git a/Kernel/Process.cpp b/Kernel/Process.cpp
index 6c933a4d9a..644de98500 100644
--- a/Kernel/Process.cpp
+++ b/Kernel/Process.cpp
@@ -458,6 +458,9 @@ int Process::sys$munmap(void* addr, size_t size)
 {
     REQUIRE_PROMISE(stdio);
 
+    if (!size)
+        return -EINVAL;
+
     if (!is_user_range(VirtualAddress(addr), size))
         return -EFAULT;
 
@@ -499,6 +502,9 @@ int Process::sys$mprotect(void* addr, size_t size, int prot)
 {
     REQUIRE_PROMISE(stdio);
 
+    if (!size)
+        return -EINVAL;
+
     if (!is_user_range(VirtualAddress(addr), size))
         return -EFAULT;
 
@@ -566,6 +572,9 @@ int Process::sys$madvise(void* address, size_t size, int advice)
 {
     REQUIRE_PROMISE(stdio);
 
+    if (!size)
+        return -EINVAL;
+
     if (!is_user_range(VirtualAddress(address), size))
         return -EFAULT;