diff --git a/AUTHORS b/AUTHORS
index da04d5c4d1..e64a2358f8 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -58,6 +58,7 @@ Ryoichi KATO         <ryo1kato@gmail.com>             - doc fixes
 Rémy Léone           <remy.leone@gmail.com>           - add .travis.yml
 Santiago Lapresta    <santiago.lapresta@gmail.com>    - join, arrays, all, any, other filters
 Sebastian Freundt    <freundt@ga-group.nl>            - build
+Shaun Guth           <shaun.guth@gmail.com>           - base64d
 Shay Elkin           <shay@everything.me>
 Simon Elsbrock       <simon@iodev.org>                - Debian
 Stefan Seemayer      <stefan@seemayer.de>
diff --git a/Makefile.am b/Makefile.am
index c1eaf6deca..cf5d74dc5b 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -115,7 +115,7 @@ endif
 
 ### Tests (make check)
 
-TESTS = tests/optionaltest tests/mantest tests/jqtest tests/onigtest tests/shtest tests/utf8test
+TESTS = tests/optionaltest tests/mantest tests/jqtest tests/onigtest tests/shtest tests/utf8test tests/base64test
 TESTS_ENVIRONMENT = NO_VALGRIND=$(NO_VALGRIND)
 
 
diff --git a/appveyor.yml b/appveyor.yml
index 719b4dce8e..e58981e7b2 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -26,7 +26,7 @@ build_script:
 test_script:
   # tests/optionaltest and tests/shtest fail on Windows; run them
   # anyways but ignore their failures.  Also, trace shtest.
-  - bash -lc "exec 0</dev/null && cd $APPVEYOR_BUILD_FOLDER && make -j3 'TESTS=tests/mantest tests/jqtest tests/onigtest' check"
+  - bash -lc "exec 0</dev/null && cd $APPVEYOR_BUILD_FOLDER && make -j3 'TESTS=tests/mantest tests/jqtest tests/onigtest tests/base64test' check"
   - bash -lc "exec 0</dev/null && cd $APPVEYOR_BUILD_FOLDER && make TESTS=tests/optionaltest check || cat test-suite.log"
   - bash -lc "exec 0</dev/null && cd $APPVEYOR_BUILD_FOLDER && make TRACE_TESTS=1 TESTS=tests/shtest check || cat test-suite.log"
       
diff --git a/docs/content/3.manual/manual.yml b/docs/content/3.manual/manual.yml
index baad2ad3ce..0f91742662 100644
--- a/docs/content/3.manual/manual.yml
+++ b/docs/content/3.manual/manual.yml
@@ -1770,6 +1770,11 @@ sections:
 
             The input is converted to base64 as specified by RFC 4648.
 
+          * `@base64d`:
+
+            The inverse of `@base64`, input is decoded as specified by RFC 4648.
+            Note\: If the decoded string is not UTF-8, the results are undefined.
+
           This syntax can be combined with string interpolation in a
           useful way. You can follow a `@foo` token with a string
           literal. The contents of the string literal will *not* be
@@ -1799,6 +1804,14 @@ sections:
             input: "\"O'Hara's Ale\""
             output: ["\"echo 'O'\\\\''Hara'\\\\''s Ale'\""]
 
+          - program: '@base64'
+            input: '"This is a message"'
+            output: ['"VGhpcyBpcyBhIG1lc3NhZ2U="']
+
+          - program: '@base64d'
+            input: '"VGhpcyBpcyBhIG1lc3NhZ2U="'
+            output: ['"This is a message"']
+
       - title: "Dates"
         body: |
 
diff --git a/src/builtin.c b/src/builtin.c
index aa0ab4d5eb..24e311e113 100644
--- a/src/builtin.c
+++ b/src/builtin.c
@@ -396,6 +396,24 @@ static jv f_utf8bytelength(jq_state *jq, jv input) {
 
 #define CHARS_ALPHANUM "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
 
+static const unsigned char BASE64_ENCODE_TABLE[64 + 1] = CHARS_ALPHANUM "+/";
+static const unsigned char BASE64_INVALID_ENTRY = 0xFF;
+static const unsigned char BASE64_DECODE_TABLE[255] = {
+  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+  62, // +
+  0xFF, 0xFF, 0xFF,
+  63, // /
+  52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // 0-9
+  0xFF, 0xFF, 0xFF,
+  99, // =
+  0xFF, 0xFF, 0xFF,
+  0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // A-Z
+  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+  26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,  // a-z
+  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF
+};
+
+
 static jv escape_string(jv input, const char* escapings) {
 
   assert(jv_get_kind(input) == JV_KIND_STRING);
@@ -548,7 +566,6 @@ static jv f_format(jq_state *jq, jv input, jv fmt) {
     jv_free(fmt);
     input = f_tostring(jq, input);
     jv line = jv_string("");
-    const char b64[64 + 1] = CHARS_ALPHANUM "+/";
     const unsigned char* data = (const unsigned char*)jv_string_value(input);
     int len = jv_string_length_bytes(jv_copy(input));
     for (int i=0; i<len; i+=3) {
@@ -560,7 +577,7 @@ static jv f_format(jq_state *jq, jv input, jv fmt) {
       }
       char buf[4];
       for (int j=0; j<4; j++) {
-        buf[j] = b64[(code >> (18 - j*6)) & 0x3f];
+        buf[j] = BASE64_ENCODE_TABLE[(code >> (18 - j*6)) & 0x3f];
       }
       if (n < 3) buf[3] = '=';
       if (n < 2) buf[2] = '=';
@@ -568,6 +585,49 @@ static jv f_format(jq_state *jq, jv input, jv fmt) {
     }
     jv_free(input);
     return line;
+  } else if (!strcmp(fmt_s, "base64d")) {
+    jv_free(fmt);
+    input = f_tostring(jq, input);
+    const unsigned char* data = (const unsigned char*)jv_string_value(input);
+    int len = jv_string_length_bytes(jv_copy(input));
+    size_t decoded_len = (3 * len) / 4; // 3 usable bytes for every 4 bytes of input
+    char *result = malloc(decoded_len * sizeof(char));
+    memset(result, 0, decoded_len * sizeof(char));
+    uint32_t ri = 0;
+    int input_bytes_read=0;
+    uint32_t code = 0;
+    for (int i=0; i<len && data[i] != '='; i++) {
+      if (BASE64_DECODE_TABLE[data[i]] == BASE64_INVALID_ENTRY) {
+        free(result);
+        return type_error(input, "is not valid base64 data");
+      }
+
+      code <<= 6;
+      code |= BASE64_DECODE_TABLE[data[i]];
+      input_bytes_read++;
+
+      if (input_bytes_read == 4) {
+        result[ri++] = (code >> 16) & 0xFF;
+        result[ri++] = (code >> 8) & 0xFF;
+        result[ri++] = code & 0xFF;
+        input_bytes_read = 0;
+        code = 0;
+      }
+    }
+    if (input_bytes_read == 3) {
+      result[ri++] = (code >> 10) & 0xFF;
+      result[ri++] = (code >> 2) & 0xFF;
+    } else if (input_bytes_read == 2) {
+      result[ri++] = (code >> 4) & 0xFF;
+    } else if (input_bytes_read == 1) {
+      free(result);
+      return type_error(input, "trailing base64 byte found");
+    }
+
+    jv line = jv_string_sized(result, ri);
+    jv_free(input);
+    free(result);
+    return line;
   } else {
     jv_free(input);
     return jv_invalid_with_msg(jv_string_concat(fmt, jv_string(" is not a valid format")));
diff --git a/tests/base64.test b/tests/base64.test
new file mode 100644
index 0000000000..0f82b0b71d
--- /dev/null
+++ b/tests/base64.test
@@ -0,0 +1,35 @@
+# Tests are groups of three lines: program, input, expected output
+# Blank lines and lines starting with # are ignored
+
+@base64
+"<>&'\"\t"
+"PD4mJyIJ"
+
+# decoding encoded output results in same text
+(@base64|@base64d)
+"<>&'\"\t"
+"<>&'\"\t"
+
+# regression test for #436
+@base64
+"foóbar\n"
+"Zm/Ds2Jhcgo="
+
+@base64d
+"Zm/Ds2Jhcgo="
+"foóbar\n"
+
+# optional trailing equals padding (With padding, this is cWl4YmF6Cg==)
+@base64d
+"cWl4YmF6Cg"
+"qixbaz\n"
+
+# invalid base64 characters (whitespace)
+. | try @base64d catch .
+"Not base64 data"
+"string (\"Not base64...) is not valid base64 data"
+
+# invalid base64 (too many bytes, QUJD = "ABCD"
+. | try @base64d catch .
+"QUJDa"
+"string (\"QUJDa\") trailing base64 byte found"
diff --git a/tests/base64test b/tests/base64test
new file mode 100755
index 0000000000..85fe64b719
--- /dev/null
+++ b/tests/base64test
@@ -0,0 +1,5 @@
+#!/bin/sh
+
+. "${0%/*}/setup" "$@"
+
+$VALGRIND $Q $JQ -L "$mods" --run-tests $JQTESTDIR/base64.test
diff --git a/tests/jq.test b/tests/jq.test
index fa02b6d722..f510a917e5 100644
--- a/tests/jq.test
+++ b/tests/jq.test
@@ -61,7 +61,7 @@ null
 null
 "interpolation"
 
-@text,@json,([1,.] | (@csv, @tsv)),@html,@uri,@sh,@base64
+@text,@json,([1,.] | (@csv, @tsv)),@html,@uri,@sh,@base64,(@base64 | @base64d)
 "<>&'\"\t"
 "<>&'\"\t"
 "\"<>&'\\\"\\t\""
@@ -71,12 +71,17 @@ null
 "%3C%3E%26'%22%09"
 "'<>&'\\''\"\t'"
 "PD4mJyIJ"
+"<>&'\"\t"
 
 # regression test for #436
 @base64
 "foóbar\n"
 "Zm/Ds2Jhcgo="
 
+@base64d
+"Zm/Ds2Jhcgo="
+"foóbar\n"
+
 @uri
 "\u03bc"
 "%CE%BC"