diff --git a/test/blackbox-tests/test-cases/cxx-flags.t/run.t b/test/blackbox-tests/test-cases/cxx-flags.t/run.t
index 6e7bd03e1490..ce930351696b 100644
--- a/test/blackbox-tests/test-cases/cxx-flags.t/run.t
+++ b/test/blackbox-tests/test-cases/cxx-flags.t/run.t
@@ -2,24 +2,15 @@
   > (lang dune 2.8)
   > EOF
 
+  $ GCCF="-x c++ -lstdc++ -shared-libgcc"
+  $ ClangF="-x c++"
+  $ MsvcF="/TP"
+
 Default: add_cxx_flags = false
-  $ dune rules baz.o | sed -n -e '/(action/,$p' |
-  > sed 's#'$(opam config var prefix)'#OPAM_PREFIX#'
-   (action
-    (chdir
-     _build/default
-     (run
-      /usr/bin/cc
-      -O2
-      -fno-strict-aliasing
-      -fwrapv
-      -g
-      -I
-      OPAM_PREFIX/lib/ocaml
-      -o
-      baz.o
-      -c
-      baz.cpp))))
+  $ dune rules baz.o | tr -s '\n' ' ' |
+  > grep -ce "$GCCF\|$ClangF|$MsvcF"
+  0
+  [1]
 
 
 With add_cxx_flags = false
@@ -28,23 +19,10 @@ With add_cxx_flags = false
   > (new_foreign_flags_handling false)
   > EOF
 
-  $ dune rules baz.o | sed -n -e '/(action/,$p' |
-  > sed 's#'$(opam config var prefix)'#OPAM_PREFIX#'
-   (action
-    (chdir
-     _build/default
-     (run
-      /usr/bin/cc
-      -O2
-      -fno-strict-aliasing
-      -fwrapv
-      -g
-      -I
-      OPAM_PREFIX/lib/ocaml
-      -o
-      baz.o
-      -c
-      baz.cpp))))
+  $ dune rules baz.o | tr -s '\n' ' ' |
+  > grep -ce "$GCCF\|$ClangF|$MsvcF"
+  0
+  [1]
 
 With add_cxx_flags = true
   $ cat >dune-project <<EOF
@@ -52,25 +30,9 @@ With add_cxx_flags = true
   > (new_foreign_flags_handling true)
   > EOF
 
-  $ dune rules baz.o | sed -n -e '/(action/,$p' |
-  > sed 's#'$(opam config var prefix)'#OPAM_PREFIX#'
-   (action
-    (chdir
-     _build/default
-     (run
-      /usr/bin/cc
-      -x
-      c++
-      -O2
-      -fno-strict-aliasing
-      -fwrapv
-      -g
-      -I
-      OPAM_PREFIX/lib/ocaml
-      -o
-      baz.o
-      -c
-      baz.cpp))))
+  $ dune rules baz.o  | tr -s '\n' ' ' |
+  > grep -ce "$GCCF\|$ClangF|$MsvcF"
+  1
 
   $ dune exec ./main.exe
   2046