diff --git a/Kernel/Process.cpp b/Kernel/Process.cpp
index 2c4b43e183..9887772a10 100644
--- a/Kernel/Process.cpp
+++ b/Kernel/Process.cpp
@@ -33,6 +33,7 @@
 #include <Kernel/StdLib.h>
 #include <Kernel/Syscall.h>
 #include <Kernel/TTY/MasterPTY.h>
+#include <Kernel/Thread.h>
 #include <Kernel/VM/InodeVMObject.h>
 #include <LibC/errno_numbers.h>
 #include <LibC/signal_numbers.h>
@@ -379,6 +380,18 @@ int Process::do_exec(String path, Vector<String> arguments, Vector<String> envir
         ASSERT_NOT_REACHED();
     }
 
+    size_t total_blob_size = 0;
+    for (auto& a : arguments)
+        total_blob_size += a.length() + 1;
+    for (auto& e : environment)
+        total_blob_size += e.length() + 1;
+
+    size_t total_meta_size = sizeof(char*) * (arguments.size() + 1) + sizeof(char*) * (environment.size() + 1);
+
+    // FIXME: How much stack space does process startup need?
+    if ((total_blob_size + total_meta_size) >= Thread::default_userspace_stack_size)
+        return -E2BIG;
+
     auto parts = path.split('/');
     if (parts.is_empty())
         return -ENOENT;
diff --git a/Kernel/Thread.cpp b/Kernel/Thread.cpp
index 8963b2b54c..467c4903ca 100644
--- a/Kernel/Thread.cpp
+++ b/Kernel/Thread.cpp
@@ -40,9 +40,6 @@ HashTable<Thread*>& thread_table()
     return *table;
 }
 
-static const u32 default_kernel_stack_size = 65536;
-static const u32 default_userspace_stack_size = 65536;
-
 Thread::Thread(Process& process)
     : m_process(process)
     , m_tid(process.m_next_tid++)
@@ -515,17 +512,6 @@ void Thread::make_userspace_stack_for_main_thread(Vector<String> arguments, Vect
     char** env = argv + arguments.size() + 1;
     char* bufptr = stack_base + (sizeof(char*) * (arguments.size() + 1)) + (sizeof(char*) * (environment.size() + 1));
 
-    size_t total_blob_size = 0;
-    for (auto& a : arguments)
-        total_blob_size += a.length() + 1;
-    for (auto& e : environment)
-        total_blob_size += e.length() + 1;
-
-    size_t total_meta_size = sizeof(char*) * (arguments.size() + 1) + sizeof(char*) * (environment.size() + 1);
-
-    // FIXME: It would be better if this didn't make us panic.
-    ASSERT((total_blob_size + total_meta_size) < default_userspace_stack_size);
-
     for (int i = 0; i < arguments.size(); ++i) {
         argv[i] = bufptr;
         memcpy(bufptr, arguments[i].characters(), arguments[i].length());
diff --git a/Kernel/Thread.h b/Kernel/Thread.h
index dc728f9d35..baeb85146d 100644
--- a/Kernel/Thread.h
+++ b/Kernel/Thread.h
@@ -1,10 +1,10 @@
 #pragma once
 
-#include <AK/String.h>
 #include <AK/Function.h>
 #include <AK/IntrusiveList.h>
 #include <AK/OwnPtr.h>
 #include <AK/RefPtr.h>
+#include <AK/String.h>
 #include <AK/Vector.h>
 #include <Kernel/Arch/i386/CPU.h>
 #include <Kernel/KResult.h>
@@ -312,6 +312,9 @@ public:
         return state == Thread::State::Running || state == Thread::State::Runnable;
     }
 
+    static constexpr u32 default_kernel_stack_size = 65536;
+    static constexpr u32 default_userspace_stack_size = 65536;
+
 private:
     IntrusiveListNode m_runnable_list_node;
 
diff --git a/Libraries/LibC/limits.h b/Libraries/LibC/limits.h
index 63156af450..08d8148381 100644
--- a/Libraries/LibC/limits.h
+++ b/Libraries/LibC/limits.h
@@ -6,7 +6,7 @@
 
 #define PATH_MAX 4096
 #if !defined MAXPATHLEN && defined PATH_MAX
-# define MAXPATHLEN  PATH_MAX
+#    define MAXPATHLEN PATH_MAX
 #endif
 
 #define INT_MAX INT32_MAX
@@ -30,3 +30,5 @@
 #define CHAR_MAX SCHAR_MAX
 
 #define MB_LEN_MAX 16
+
+#define ARG_MAX 65536