diff --git a/test/run b/test/run
index cf71259b..88202916 100755
--- a/test/run
+++ b/test/run
@@ -16,7 +16,13 @@ else
   test_dirs=( "$1" )
 fi
 
-if command -v parallel &> /dev/null
+# Make sure that the `parallel` command is installed,
+# AND that it is the GNU version of `parallel`.
+# If that is the case, try to guess the number of CPU cores,
+# so we can run `bats` in parallel processing mode, which is a lot faster.
+if command -v parallel &> /dev/null \
+  && parallel -V &> /dev/null \
+  && { parallel -V 2> /dev/null | grep -q '^GNU\>'; }
 then
   # Expect to run at least on a dual-core CPU; slightly degraded performance
   # shouldn't matter otherwise.
@@ -37,5 +43,6 @@ then
   exec "$bats_executable" ${CI:+--tap} --jobs ${test_jobs_effective} \
     "${test_dirs[@]}"
 else
+  # Run `bats` in single-threaded mode.
   exec "$bats_executable" ${CI:+--tap} "${test_dirs[@]}"
 fi