diff --git a/pipreqs/lint_mapping.sh b/pipreqs/lint_mapping.sh
new file mode 100755
index 0000000..126f9c0
--- /dev/null
+++ b/pipreqs/lint_mapping.sh
@@ -0,0 +1,58 @@
+#!/usr/bin/bash
+# ------------------------------------------------------------------------------
+# Author      : Michael Wurm <wurm.michael95@gmail.com>
+# Description : Formats mapping to lowercase and removes duplicate
+#               entries from the mappings file.
+# ------------------------------------------------------------------------------
+
+# Script setup
+
+SCRIPT_PATH=$(cd -- "$(dirname -- "$(readlink -f "${BASH_SOURCE[0]}" || ${BASH_SOURCE[0]})")" &>/dev/null && pwd)
+cd "$SCRIPT_PATH"
+
+set -euo pipefail
+
+# Functions
+
+convert_file_to_lowercase() {
+    FILE_MIXED=mapping
+    FILE_LOWER=mapping.new
+
+    tr '[:upper:]' '[:lower:]' <$FILE_MIXED >$FILE_LOWER
+
+    mv $FILE_LOWER $FILE_MIXED
+    echo "Converted entire file to lowercase"
+}
+
+filter_duplicates() {
+    # Loop through the original file line by line.
+    # Write each line into a new file.
+    # Skip lines with a duplicate mapping, i.e. abc:abc
+
+    MAPPING_OLD="$SCRIPT_PATH/mapping"
+    MAPPING_NEW="$SCRIPT_PATH/mapping.new"
+
+    i=0
+    found=0
+    while IFS= read -r line; do
+        ((i = i + 1))
+        mapelements=($(echo "$line" | tr ':' '\n'))
+        if [ "${mapelements[0]}" == "${mapelements[1]}" ]; then
+            echo "Found a duplicate mapping in line #$i: '$line'"
+            ((found = found + 1))
+            continue
+        fi
+        echo "$line" >>"$MAPPING_NEW"
+    done <"$MAPPING_OLD"
+
+    echo "---"
+    mv "$MAPPING_NEW" "$MAPPING_OLD"
+    echo "Removed $found duplicates."
+}
+
+main() {
+    convert_file_to_lowercase
+    filter_duplicates
+}
+
+main