diff --git a/src/base64.cc b/src/base64.cc
index f54ddaed..fe8fbbae 100644
--- a/src/base64.cc
+++ b/src/base64.cc
@@ -16,6 +16,8 @@
 
 #include "base64.h"
 
+#include <vector>
+
 namespace base64 {
 
 namespace {
@@ -27,21 +29,23 @@ constexpr const unsigned char base64url_chars[] =
 std::string Encode(const std::string &source) {
   std::string result;
 #if 0
-  const std::size_t remainder = source.size() % 3;
+  const std::size_t remainder = (source.size() - 1) % 3;
   for (std::size_t i = 0; i < source.size(); i += 3) {
+    const bool one_more = i < source.size() - 3 || remainder > 0;
+    const bool two_more = i < source.size() - 3 || remainder > 1;
     const unsigned char c0 = source[i];
-    const unsigned char c1 = remainder > 0 ? source[i + 1] : 0u;
-    const unsigned char c2 = remainder > 1 ? source[i + 2] : 0u;
+    const unsigned char c1 = one_more ? source[i + 1] : 0u;
+    const unsigned char c2 = two_more ? source[i + 2] : 0u;
     result.push_back(base64url_chars[0x3f & c0 >> 2]);
-    result.push_back(base64url_chars[0x3f & c0 << 4 | c1 >> 4]);
-    if (remainder > 0) {
-      result.push_back(base64url_chars[0x3f & c1 << 2 | c2 >> 6]);
+    result.push_back(base64url_chars[(0x3f & c0 << 4) | c1 >> 4]);
+    if (one_more) {
+      result.push_back(base64url_chars[(0x3f & c1 << 2) | c2 >> 6]);
     }
-    if (remainder > 1) {
+    if (two_more) {
       result.push_back(base64url_chars[0x3f & c2]);
     }
   }
-#endif
+#else
   unsigned int code_buffer = 0;
   int code_buffer_size = -6;
   for (unsigned char c : source) {
@@ -57,30 +61,29 @@ std::string Encode(const std::string &source) {
     code_buffer_size += 8;
     result.push_back(base64url_chars[(code_buffer >> code_buffer_size) & 0x3f]);
   }
+#endif
   // No padding needed.
   return result;
 }
 
-#if 0
 std::string Decode(const std::string &source) {
   std::string result;
 
-  std::vector<int> T(256,-1);
-  for (int i=0; i<64; i++) T[base64url_chars[i]] = i;
+  std::vector<int> T(256, -1);
+  for (int i = 0; i < 64; i++) T[base64url_chars[i]] = i;
 
-  int val=0, valb=-8;
-  for (uchar c : source) {
+  int val = 0, shift = -8;
+  for (char c : source) {
     if (T[c] == -1) break;
-    val = (val<<6) + T[c];
-    valb += 6;
-    if (valb>=0) {
-      result.push_back(char((val>>valb)&0xFF));
-      valb-=8;
+    val = (val << 6) + T[c];
+    shift += 6;
+    if (shift >= 0) {
+      result.push_back(char((val >> shift) & 0xFF));
+      shift -= 8;
     }
   }
   return result;
 }
-#endif
 
 }
 
diff --git a/test/Makefile b/test/Makefile
index efb58a36..5b33fc2a 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -21,7 +21,8 @@ TEST_DIR=.
 TEST_SOURCES=$(wildcard $(TEST_DIR)/*_unittest.cc)
 TEST_OBJS=$(TEST_SOURCES:$(TEST_DIR)/%.cc=%.o)
 TESTS=\
-      format_unittest
+      format_unittest \
+      base64_unittest
 
 GTEST_LIB=gtest_lib.a
 
@@ -63,5 +64,7 @@ $(GTEST_LIB): gtest-all.o gtest_main.o
 
 format_unittest: $(GTEST_LIB) format_unittest.o $(SRC_DIR)/format.o
 	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
+base64_unittest: $(GTEST_LIB) base64_unittest.o $(SRC_DIR)/base64.o
+	$(CXX) $(LDFLAGS) $^ $(LDLIBS) -o $@
 
 .PHONY: all test clean purge
diff --git a/test/base64_unittest.cc b/test/base64_unittest.cc
new file mode 100644
index 00000000..57f331d2
--- /dev/null
+++ b/test/base64_unittest.cc
@@ -0,0 +1,61 @@
+#include "../src/base64.h"
+#include "gtest/gtest.h"
+
+namespace {
+
+TEST(EncodeTest, EmptyEncode) {
+  EXPECT_EQ("", base64::Encode(""));
+}
+
+TEST(EncodeTest, SimpleEncode) {
+  EXPECT_EQ("dGVz", base64::Encode("tes"));
+}
+
+// Base64 encoders typically pad messages to ensure output length % 4 == 0. To
+// achieve this, encoders will pad messages with either one or two "=". Our
+// implementation does not do this. The following two tests ensure that
+// base64::Encode does not append one or two "=".
+TEST(EncodeTest, OnePhantom) {
+  EXPECT_EQ("dGVzdDA", base64::Encode("test0"));
+}
+
+TEST(EncodeTest, TwoPhantom) {
+  EXPECT_EQ("dGVzdA", base64::Encode("test"));
+}
+
+TEST(DecodeTest, EmptyDecode) {
+  EXPECT_EQ("", base64::Decode(""));
+}
+
+TEST(DecodeTest, SimpleDecode) {
+  EXPECT_EQ("tes", base64::Decode("dGVz"));
+}
+
+TEST(DecodeTest, OnePadding) {
+  EXPECT_EQ("test0", base64::Decode("dGVzdDA="));
+}
+
+TEST(DecodeTest, OnePhantom) {
+  EXPECT_EQ("test0", base64::Decode("dGVzdDA"));
+}
+
+TEST(DecodeTest, TwoPadding) {
+  EXPECT_EQ("test", base64::Decode("dGVzdA=="));
+}
+
+TEST(DecodeTest, TwoPhantom) {
+  EXPECT_EQ("test", base64::Decode("dGVzdA"));
+}
+
+TEST(RoundTripTest, FullString) {
+  EXPECT_EQ("tes", base64::Decode(base64::Encode("tes")));
+}
+
+TEST(RoundTripTest, OnePhantom) {
+  EXPECT_EQ("test0", base64::Decode(base64::Encode("test0")));
+}
+
+TEST(RoundTripTest, TwoPhantoms) {
+  EXPECT_EQ("test", base64::Decode(base64::Encode("test")));
+}
+} // namespace