diff --git a/README.md b/README.md
index f7786f0..de7ca75 100644
--- a/README.md
+++ b/README.md
@@ -55,7 +55,14 @@ cpn("aa", "ab", "abc", "abd") = "a{a,b{,c,d}}"
 cpn("a", "ab", "abc") = "{a{,b{,c}}}"
 ```
 
-*Note:* For the sake of reasoning, strings containing the CPN’s reserved characters {, } and , shall be considered invalid input. In a practical implementation, a syntax for „escaping“ these reserved characters should be available. For example, in the reference implementation, the print_trie() function inserts a backslash character \ in front of every literal {, , and }.
+*Note:* For the sake of reasoning, strings containing the CPN’s reserved
+characters `{`, `}` and , shall be considered invalid input. In a practical
+implementation, a syntax for „escaping“ these reserved characters should be
+available. For example, in the reference implementation, the `print_trie()`
+function inserts a backslash character `\` in front of every literal `{`, `,`
+and `}`; additionally, every space character ` ` is escaped, because it
+acts as a word separator in GNU Bourne Again Shell and other interpreters
+of brace expansion syntax.
 
 ## 2 Implementation
 
@@ -95,8 +102,3 @@ Expected output:
 a ab abc
 ```
 
-## Appendix A: References
-
-* [Initial announcement](https://tk-sls.de/wp/6071)
-* [Update](https://tk-sls.de/wp/6144)
-* [Git repository](https://tk-sls.de/gitlab/tilman/trie)
diff --git a/test/01.sh b/test/01.sh
new file mode 100755
index 0000000..fad4667
--- /dev/null
+++ b/test/01.sh
@@ -0,0 +1,26 @@
+#!/bin/bash
+
+dir=$(dirname "$(readlink -f "$0")")
+trie="$dir/../trie.py"
+
+read -r -d '' input <<EOF
+a b x
+a b c
+a b c d
+EOF
+
+output=$(echo "$input" | "$trie")
+
+# shellcheck disable=SC2086
+result=$(eval 'for i in '$output' ; do echo "$i" ; done' | sort)
+
+reference=$(echo "$input" | sort | uniq)
+
+if test "$reference" = "$result" ; then
+    rv=0
+else
+    printf 'ERROR: reference=\n%s\nresult=\n%s\n' "$reference" "$result"
+    rv=1
+fi
+
+exit $rv
diff --git a/trie.py b/trie.py
old mode 100644
new mode 100755
index 6ad1d86..20bd4ee
--- a/trie.py
+++ b/trie.py
@@ -34,7 +34,7 @@ def print_trie(trie):
     count = 1
 
     for k in trie:
-        if k == '{' or k == ',' or k == '}':
+        if k == '{' or k == ',' or k == '}' or k == ' ':
             sys.stdout.write('\\')
 
         sys.stdout.write(k)