diff --git a/lib/spack/spack/hooks/sbang.py b/lib/spack/spack/hooks/sbang.py
index 1c18c46dc65..ce2cf3435d2 100644
--- a/lib/spack/spack/hooks/sbang.py
+++ b/lib/spack/spack/hooks/sbang.py
@@ -110,6 +110,10 @@ def filter_shebang(path):
         # Store the file permissions, the patched version needs the same.
         saved_mode = os.stat(path).st_mode
 
+        # Change non-writable files to be writable if needed.
+        if not os.access(path, os.W_OK):
+            os.chmod(path, saved_mode | stat.S_IWUSR)
+
         # No need to delete since we'll move it and overwrite the original.
         patched = tempfile.NamedTemporaryFile('wb', delete=False)
         patched.write(new_sbang_line)
diff --git a/lib/spack/spack/test/sbang.py b/lib/spack/spack/test/sbang.py
index e9beebc43d5..6d26bd1ba87 100644
--- a/lib/spack/spack/test/sbang.py
+++ b/lib/spack/spack/test/sbang.py
@@ -374,3 +374,14 @@ def test_shebang_exceeds_spack_shebang_limit(shebang_limits_system_8_spack_16, t
 
     with open(file, 'rb') as f:
         assert b'sbang' not in f.read()
+
+
+def test_sbang_hook_handles_non_writable_files_preserving_permissions(tmpdir):
+    path = str(tmpdir.join('file.sh'))
+    with open(path, 'w') as f:
+        f.write(long_line)
+    os.chmod(path, 0o555)
+    sbang.filter_shebang(path)
+    with open(path, 'r') as f:
+        assert 'sbang' in f.readline()
+    assert os.stat(path).st_mode & 0o777 == 0o555