diff --git a/share/spack/qa/run-unit-tests b/share/spack/qa/run-unit-tests
index f724c864c8..3498b3a416 100755
--- a/share/spack/qa/run-unit-tests
+++ b/share/spack/qa/run-unit-tests
@@ -52,7 +52,7 @@ if [[ "$SPACK_TEST_SOLVER" == "original" ]]; then
 fi
 
 # Check if xdist is available
-if python -m pytest -VV 2>&1 | grep xdist; then
+if [[ "$UNIT_TEST_COVERAGE" != "true" ]] && python -m pytest -VV 2>&1 | grep xdist; then
   export PYTEST_ADDOPTS="$PYTEST_ADDOPTS --dist loadfile --tx '${SPACK_TEST_PARALLEL:=3}*popen//python=./bin/spack-tmpconfig python -u ./bin/spack python'"
 fi
 
@@ -66,9 +66,9 @@ fi
 # where it seems that otherwise the configuration file might not be located by subprocesses
 # in some, not better specified, cases.
 if [[ "$UNIT_TEST_COVERAGE" == "true" ]]; then
-  $(which spack) unit-test -x --verbose --cov --cov-config=pyproject.toml --cov-report=xml:coverage.xml
+  "$(which spack)" unit-test -x --verbose --cov --cov-config=pyproject.toml --cov-report=xml:coverage.xml
 else
-  $(which spack) unit-test -x --verbose
+  "$(which spack)" unit-test -x --verbose
 fi