diff --git a/Makefile.am b/Makefile.am
index f870182..8710d74 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -34,6 +34,7 @@ TESTS = \
 	tests/encode.sh \
 	tests/encode-b58c.sh \
 	tests/encode-fail.sh \
+	tests/encode-neg-index.sh \
 	tests/encode-small.sh
 SH_LOG_COMPILER = /bin/sh
 AM_TESTS_ENVIRONMENT = PATH='$(srcdir)':"$$PATH"; export PATH;
diff --git a/tests/encode-neg-index.sh b/tests/encode-neg-index.sh
new file mode 100755
index 0000000..79622c2
--- /dev/null
+++ b/tests/encode-neg-index.sh
@@ -0,0 +1,4 @@
+#!/bin/sh
+# This input causes the loop iteration counter to go negative
+b58=$(echo '00CEF022FA' | xxd -r -p | base58)
+test x$b58 = x16Ho7Hs