diff --git a/.ci/test-r-package.sh b/.ci/test-r-package.sh
index 9525a9bf35ea..7d821676bb71 100755
--- a/.ci/test-r-package.sh
+++ b/.ci/test-r-package.sh
@@ -181,12 +181,11 @@ elif [[ $R_BUILD_TYPE == "cran" ]]; then
 
         # the exceptions below are from R itself and not LightGBM:
         # https://github.com/kalibera/rchk/issues/22#issuecomment-656036156
-        exit $(
-            cat "${RCHK_LOG_FILE}" \
-            | grep -v "in function strptime_internal" \
+        exit "$(
+            grep "${RCHK_LOG_FILE}" -v "in function strptime_internal" \
             | grep -v "in function RunGenCollect" \
             | grep --count -E '\[PB\]|ERROR'
-        )
+        )"
     fi
 
     # Test CRAN source .tar.gz in a directory that is not this repo or below it.