diff --git a/.ci/test-r-package.sh b/.ci/test-r-package.sh
index 6db0beb8293b..f60278a285ca 100755
--- a/.ci/test-r-package.sh
+++ b/.ci/test-r-package.sh
@@ -19,7 +19,7 @@ if [[ $R_BUILD_TYPE != "cran" ]]; then
 fi
 
 # Get details needed for installing R components
-R_MAJOR_VERSION=( "${R_VERSION//./ }" )
+IFS='.' read -ra R_MAJOR_VERSION <<< "$R_VERSION"
 if [[ "${R_MAJOR_VERSION[0]}" == "3" ]]; then
     export R_MAC_VERSION=3.6.3
     export R_MAC_PKG_URL=${CRAN_MIRROR}/bin/macosx/R-${R_MAC_VERSION}.nn.pkg
diff --git a/.ci/test.sh b/.ci/test.sh
index b0a8dbd0d766..99a0e3737908 100755
--- a/.ci/test.sh
+++ b/.ci/test.sh
@@ -131,9 +131,11 @@ if [[ $TASK == "check-docs" ]] || [[ $TASK == "check-links" ]]; then
     source activate $CONDA_ENV
     # check reStructuredText formatting
     cd "${BUILD_DIRECTORY}/python-package"
-    rstcheck --report-level warning "$(find . -type f -name "*.rst")" || exit 1
+    find . -type f -name "*.rst" -exec \
+        rstcheck --report-level warning {} + || exit 1
     cd "${BUILD_DIRECTORY}/docs"
-    rstcheck --report-level warning --ignore-directives=autoclass,autofunction,autosummary,doxygenfile "$(find . -type f -name "*.rst")" || exit 1
+    find . -type f -name "*.rst" -exec \
+        rstcheck --report-level warning --ignore-directives=autoclass,autofunction,autosummary,doxygenfile {} + || exit 1
     # build docs
     make html || exit 1
     if [[ $TASK == "check-links" ]]; then