diff --git a/ci/travis/cover.sh b/ci/travis/cover.sh
index 66b01f6d..8b8ee8e5 100755
--- a/ci/travis/cover.sh
+++ b/ci/travis/cover.sh
@@ -2,12 +2,14 @@
 
 set -ex
 
-### Run kcov in parallel #######################################################
+### Run kcov ###################################################################
 
 rm -f target/debug/pyo3*.d
 rm -f target/debug/test_*.d
 rm -f target/debug/test_doc-*
 
+# Note: On travis this is run with -P1 because it started failing with
+# `-P $(nproc)`. kcov can probably be run in parallel if used with different CI
 FILES=$(find . -path ./target/debug/pyo3\* -or -path ./target/debug/test_\*)
 echo $FILES | xargs -n1 -P1 sh -c '
   dir="target/cov/$(basename $@)"