diff --git a/var/spack/repos/builtin/packages/mumps/package.py b/var/spack/repos/builtin/packages/mumps/package.py
index b04a1b073c..3ba3ca26b5 100644
--- a/var/spack/repos/builtin/packages/mumps/package.py
+++ b/var/spack/repos/builtin/packages/mumps/package.py
@@ -155,8 +155,7 @@ def write_makefile_inc(self):
                 makefile_conf.extend([
                     'OPTF = %s -O  -DALLOW_NON_INIT %s' % (
                         fpic,
-                        '-fdefault-integer-8' if using_gcc
-                                              else '-i8'),  # noqa
+                        '-fdefault-integer-8' if using_gcc else '-i8'),  # noqa
                 ])
 
             makefile_conf.extend([
@@ -275,6 +274,15 @@ def write_makefile_inc(self):
                 makefile_inc = '\n'.join(makefile_conf)
                 fh.write(makefile_inc)
 
+    def flag_handler(self, name, flags):
+        if name == 'fflags':
+            if self.spec.satisfies('%gcc@10:'):
+                if flags is None:
+                    flags = []
+                flags.append('-fallow-argument-mismatch')
+
+        return (flags, None, None)
+
     def install(self, spec, prefix):
         self.write_makefile_inc()