diff --git a/system/lib/update_compiler_rt.py b/system/lib/update_compiler_rt.py
index 5f2eef86dfdbd..997d794986197 100755
--- a/system/lib/update_compiler_rt.py
+++ b/system/lib/update_compiler_rt.py
@@ -46,6 +46,10 @@ def main():
     llvm_dir = os.path.join(os.path.abspath(sys.argv[1]))
   else:
     llvm_dir = default_llvm_dir
+  if not os.path.isdir(llvm_dir):
+    print(f'LLVM directory not found: {llvm_dir}', file=sys.stderr)
+    print(f'Usage: {sys.argv[0]} [llvm_dir]', file=sys.stderr)
+    sys.exit(1)
   upstream_dir = os.path.join(llvm_dir, 'compiler-rt')
   assert os.path.exists(upstream_dir)
   upstream_src = os.path.join(upstream_dir, 'lib', 'builtins')
diff --git a/system/lib/update_libcxx.py b/system/lib/update_libcxx.py
index f8e6ee74c464a..75ca2022a0382 100755
--- a/system/lib/update_libcxx.py
+++ b/system/lib/update_libcxx.py
@@ -105,6 +105,10 @@ def main():
     llvm_dir = os.path.abspath(sys.argv[1])
   else:
     llvm_dir = default_llvm_dir
+  if not os.path.isdir(llvm_dir):
+    print(f'LLVM directory not found: {llvm_dir}', file=sys.stderr)
+    print(f'Usage: {sys.argv[0]} [llvm_dir]', file=sys.stderr)
+    sys.exit(1)
   libcxx_dir = os.path.join(llvm_dir, 'libcxx')
   upstream_src = os.path.join(libcxx_dir, 'src')
   upstream_inc = os.path.join(libcxx_dir, 'include')
diff --git a/system/lib/update_libcxxabi.py b/system/lib/update_libcxxabi.py
index a939501865563..0b8249e6e4112 100755
--- a/system/lib/update_libcxxabi.py
+++ b/system/lib/update_libcxxabi.py
@@ -44,6 +44,10 @@ def main():
     llvm_dir = os.path.join(os.path.abspath(sys.argv[1]))
   else:
     llvm_dir = default_llvm_dir
+  if not os.path.isdir(llvm_dir):
+    print(f'LLVM directory not found: {llvm_dir}', file=sys.stderr)
+    print(f'Usage: {sys.argv[0]} [llvm_dir]', file=sys.stderr)
+    sys.exit(1)
   upstream_root = os.path.join(llvm_dir, 'libcxxabi')
   upstream_src = os.path.join(upstream_root, 'src')
   upstream_inc = os.path.join(upstream_root, 'include')
diff --git a/system/lib/update_libunwind.py b/system/lib/update_libunwind.py
index f9d4ff8883f77..c52e77f242849 100755
--- a/system/lib/update_libunwind.py
+++ b/system/lib/update_libunwind.py
@@ -44,6 +44,10 @@ def main():
     llvm_dir = os.path.join(os.path.abspath(sys.argv[1]))
   else:
     llvm_dir = default_llvm_dir
+  if not os.path.isdir(llvm_dir):
+    print(f'LLVM directory not found: {llvm_dir}', file=sys.stderr)
+    print(f'Usage: {sys.argv[0]} [llvm_dir]', file=sys.stderr)
+    sys.exit(1)
   upstream_root = os.path.join(llvm_dir, 'libunwind')
   upstream_src = os.path.join(upstream_root, 'src')
   upstream_inc = os.path.join(upstream_root, 'include')
diff --git a/system/lib/update_llvm_libc.py b/system/lib/update_llvm_libc.py
old mode 100644
new mode 100755
index 8508bb792b67b..91525153283ab
--- a/system/lib/update_llvm_libc.py
+++ b/system/lib/update_llvm_libc.py
@@ -80,6 +80,10 @@ def main():
     llvm_dir = os.path.abspath(sys.argv[1])
   else:
     llvm_dir = default_llvm_dir
+  if not os.path.isdir(llvm_dir):
+    print(f'LLVM directory not found: {llvm_dir}', file=sys.stderr)
+    print(f'Usage: {sys.argv[0]} [llvm_dir]', file=sys.stderr)
+    sys.exit(1)
   libc_upstream_dir = os.path.join(llvm_dir, 'libc')
   assert os.path.exists(libc_upstream_dir)
   libc_local_dir = os.path.join(script_dir, 'llvm-libc')
diff --git a/system/lib/update_musl.py b/system/lib/update_musl.py
index 838685c378b25..4f3a41e5879e5 100755
--- a/system/lib/update_musl.py
+++ b/system/lib/update_musl.py
@@ -73,6 +73,10 @@
   musl_dir = os.path.abspath(sys.argv[1])
 else:
   musl_dir = default_musl_dir
+if not os.path.isdir(musl_dir):
+  print(f'musl directory not found: {musl_dir}', file=sys.stderr)
+  print(f'Usage: {sys.argv[0]} [musl_dir]', file=sys.stderr)
+  sys.exit(1)
 
 
 def make_ignore(root):