diff --git a/gcc/cp/lang-specs.h b/gcc/cp/lang-specs.h
index f16279142be..8902ae1d2ed 100644
--- a/gcc/cp/lang-specs.h
+++ b/gcc/cp/lang-specs.h
@@ -52,9 +52,11 @@ along with GCC; see the file COPYING3.  If not see
       "  %{!save-temps*:%{!no-integrated-cpp:%(cpp_unique_options)}}"
       "  %{fmodules-ts:-fmodule-header %{fpreprocessed:-fdirectives-only}}"
       "  %(cc1_options) %2"
-      "  %{!S:-o %g.s%V}"
-      "  %{!fsyntax-only:%{!fmodule-*:%{!fmodules-*:%{!fdump-ada-spec*:"
-      "	     %{!o*:--output-pch=%i.gch}%W{o*:--output-pch=%*}}}}}}}}",
+      "  %{!fsyntax-only:"
+      "    %{!S:-o %g.s%V}"
+      "    %{!fmodule-*:%{!fmodules-*:%{!fdump-ada-spec*:"
+      "	         %{!o*:--output-pch=%i.gch}%W{o*:--output-pch=%*}}}}}"
+      "}}}",
      CPLUSPLUS_CPP_SPEC, 0, 0},
   {"@c++-system-header",
       "%{E|M|MM:cc1plus -E"
@@ -68,11 +70,14 @@ along with GCC; see the file COPYING3.  If not see
       "            %{fmodules-ts:-fdirectives-only}"
       " 	   %{save-temps*:%b.ii} %{!save-temps*:%g.ii}}"
       "  %{!save-temps*:%{!no-integrated-cpp:%(cpp_unique_options)}}"
-      "  %{fmodules-ts:-fmodule-header=system %{fpreprocessed:-fdirectives-only}}"
+      "  %{fmodules-ts:-fmodule-header=system"
+      "    %{fpreprocessed:-fdirectives-only}}"
       "  %(cc1_options) %2"
-      "  %{!S:-o %g.s%V}"
-      "  %{!fsyntax-only:%{!fmodule-*:%{!fmodules-*:%{!fdump-ada-spec*:"
-      "	     %{!o*:--output-pch=%i.gch}%W{o*:--output-pch=%*}}}}}}}}",
+      "  %{!fsyntax-only:"
+      "    %{!S:-o %g.s%V}"
+      "    %{!fmodule-*:%{!fmodules-*:%{!fdump-ada-spec*:"
+      "	         %{!o*:--output-pch=%i.gch}%W{o*:--output-pch=%*}}}}}"
+      "}}}",
      CPLUSPLUS_CPP_SPEC, 0, 0},
   {"@c++-user-header",
       "%{E|M|MM:cc1plus -E"
@@ -88,9 +93,11 @@ along with GCC; see the file COPYING3.  If not see
       "  %{!save-temps*:%{!no-integrated-cpp:%(cpp_unique_options)}}"
       "  %{fmodules-ts:-fmodule-header=user %{fpreprocessed:-fdirectives-only}}"
       "  %(cc1_options) %2"
-      "  %{!S:-o %g.s%V}"
-      "  %{!fsyntax-only:%{!fmodule-*:%{!fmodules-*:%{!fdump-ada-spec*:"
-      "	     %{!o*:--output-pch=%i.gch}%W{o*:--output-pch=%*}}}}}}}}",
+      "  %{!fsyntax-only:"
+      "    %{!S:-o %g.s%V}"
+      "    %{!fmodule-*:%{!fmodules-*:%{!fdump-ada-spec*:"
+      "	         %{!o*:--output-pch=%i.gch}%W{o*:--output-pch=%*}}}}}"
+      "}}}",
      CPLUSPLUS_CPP_SPEC, 0, 0},
   {"@c++",
       "%{E|M|MM:cc1plus -E %(cpp_options) %2 %(cpp_debug_options)}"
@@ -101,13 +108,16 @@ along with GCC; see the file COPYING3.  If not see
       " 	   %{save-temps*:%b.ii} %{!save-temps*:%g.ii}}"
       "  %{!save-temps*:%{!no-integrated-cpp:%(cpp_unique_options)}}"
       "  %(cc1_options) %2"
-      "  %{fmodule-only:%{!S:-o %g.s%V}}"
-      "  %{!fsyntax-only:%{!fmodule-only:%(invoke_as)}}}}}",
+      "  %{!fsyntax-only:"
+      "    %{fmodule-only:%{!S:-o %g.s%V}}"
+      "    %{!fmodule-only:%(invoke_as)}}"
+      "}}}",
       CPLUSPLUS_CPP_SPEC, 0, 0},
   {".ii", "@c++-cpp-output", 0, 0, 0},
   {"@c++-cpp-output",
       "%{!E:%{!M:%{!MM:"
       "  cc1plus -fpreprocessed %i %(cc1_options) %2"
-      "  %{fmodule-only:%{!S:-o %g.s%V}}"
-      "  %{!fsyntax-only:%{!fmodule-only:%{!fmodule-header*:"
-      "     %(invoke_as)}}}}}}", 0, 0, 0},
+      "  %{!fsyntax-only:"
+      "    %{fmodule-only:%{!S:-o %g.s%V}}"
+      "    %{!fmodule-only:%{!fmodule-header*:%(invoke_as)}}}"
+      "}}}", 0, 0, 0},
diff --git a/gcc/testsuite/g++.dg/modules/pr98591.H b/gcc/testsuite/g++.dg/modules/pr98591.H
new file mode 100644
index 00000000000..ad397de2ecb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr98591.H
@@ -0,0 +1,3 @@
+// { dg-additional-options {-fmodules-ts -fmodule-header -fsyntax-only} }
+// PR 98591 -fsyntax-only -> output filename specified twice
+// specs are hard