diff --git a/src/Base64.cc b/src/Base64.cc
index 1826ede93a..628d872c07 100644
--- a/src/Base64.cc
+++ b/src/Base64.cc
@@ -261,7 +261,7 @@ BroString* encode_base64(const BroString* s, const BroString* a)
 
 	char* outbuf = 0;
 	int outlen = 0;
-	Base64Decoder enc(0);
+	Base64Decoder enc(0, a ? a->CheckString() : "");
 	enc.Encode(s->Len(), (const unsigned char*) s->Bytes(), &outlen, &outbuf);
 
 	return new BroString(1, (u_char*)outbuf, outlen);
diff --git a/testing/btest/Baseline/bifs.encode_base64/out b/testing/btest/Baseline/bifs.encode_base64/out
new file mode 100644
index 0000000000..84c2c98264
--- /dev/null
+++ b/testing/btest/Baseline/bifs.encode_base64/out
@@ -0,0 +1,6 @@
+YnJv
+YnJv
+}n-v
+cGFkZGluZw==
+cGFkZGluZzE=
+cGFkZGluZzEy
diff --git a/testing/btest/bifs/encode_base64.bro b/testing/btest/bifs/encode_base64.bro
new file mode 100644
index 0000000000..a351392bb5
--- /dev/null
+++ b/testing/btest/bifs/encode_base64.bro
@@ -0,0 +1,14 @@
+# @TEST-EXEC: bro -b %INPUT >out
+# @TEST-EXEC: btest-diff out
+
+global default_alphabet: string = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+global my_alphabet: string = "!#$%&/(),-.:;<>@[]^ `_{|}~abcdefghijklmnopqrstuvwxyz0123456789+?";
+
+print encode_base64("bro");
+print encode_base64_custom("bro", default_alphabet);
+print encode_base64_custom("bro", my_alphabet);
+
+print encode_base64("padding");
+print encode_base64("padding1");
+print encode_base64("padding12");