diff --git a/distrho/extra/String.hpp b/distrho/extra/String.hpp
index 015ff49e..7364662d 100644
--- a/distrho/extra/String.hpp
+++ b/distrho/extra/String.hpp
@@ -699,7 +699,7 @@ public:
         char* strBuf = static_cast<char*>(std::malloc(strBufSize));
         DISTRHO_SAFE_ASSERT_RETURN(strBuf != nullptr, String());
 
-        strBuf[strBufSize] = '\0';
+        strBuf[strBufSize - 1] = '\0';
         size_t strBufIndex = 0;
 
         const uchar* bytesToEncode = static_cast<const uchar*>(data);
diff --git a/tests/Base64.cpp b/tests/Base64.cpp
new file mode 100644
index 00000000..b032b2a7
--- /dev/null
+++ b/tests/Base64.cpp
@@ -0,0 +1,36 @@
+/*
+ * DISTRHO Plugin Framework (DPF)
+ * Copyright (C) 2012-2025 Filipe Coelho <falktx@falktx.com>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any purpose with
+ * or without fee is hereby granted, provided that the above copyright notice and this
+ * permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD
+ * TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN
+ * NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+ * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#define HEADLESS_TESTS
+#include "tests.hpp"
+#include "distrho/extra/Base64.hpp"
+#include "distrho/extra/String.hpp"
+
+// --------------------------------------------------------------------------------------------------------------------
+
+int main()
+{
+    using namespace DISTRHO_NAMESPACE;
+
+    String test("This is a test");
+    std::vector<uint8_t> testblob(test.buffer(), test.buffer() + (test.length() + 1));
+    std::vector<uint8_t> blob = d_getChunkFromBase64String(String::asBase64(test.buffer(), test.length() + 1));
+    DISTRHO_ASSERT_EQUAL(blob, testblob, "encode + decode must match original data");
+
+    return 0;
+}
+
+// --------------------------------------------------------------------------------------------------------------------
diff --git a/tests/Makefile b/tests/Makefile
index cda9a433..2be6d2ef 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -24,7 +24,7 @@ endif
 # ---------------------------------------------------------------------------------------------------------------------
 
 MANUAL_TESTS  =
-UNIT_TESTS    = Color Point
+UNIT_TESTS    = Base64 Color Point
 
 ifeq ($(HAVE_CAIRO),true)
 MANUAL_TESTS += Demo.cairo
diff --git a/tests/tests.hpp b/tests/tests.hpp
index e114f22e..00d25367 100644
--- a/tests/tests.hpp
+++ b/tests/tests.hpp
@@ -1,6 +1,6 @@
 /*
  * DISTRHO Plugin Framework (DPF)
- * Copyright (C) 2012-2024 Filipe Coelho <falktx@falktx.com>
+ * Copyright (C) 2012-2025 Filipe Coelho <falktx@falktx.com>
  *
  * Permission to use, copy, modify, and/or distribute this software for any purpose with
  * or without fee is hereby granted, provided that the above copyright notice and this
@@ -16,10 +16,6 @@
 
 #pragma once
 
-#include "dgl/Application.hpp"
-
-#include "distrho/extra/Thread.hpp"
-
 #define DISTRHO_ASSERT_EQUAL(v1, v2, msg) \
     if (v1 != v2) { d_stderr2("Test condition failed: %s; file:%s line:%i", msg, __FILE__, __LINE__); return 1; }
 
@@ -29,6 +25,11 @@
 #define DISTRHO_ASSERT_SAFE_EQUAL(v1, v2, msg) \
     if (d_isNotEqual(v1, v2)) { d_stderr2("Test condition failed: %s; file:%s line:%i", msg, __FILE__, __LINE__); return 1; }
 
+#ifndef HEADLESS_TESTS
+
+#include "dgl/Application.hpp"
+#include "distrho/extra/Thread.hpp"
+
 START_NAMESPACE_DGL
 
 // --------------------------------------------------------------------------------------------------------------------
@@ -59,3 +60,5 @@ private:
 // --------------------------------------------------------------------------------------------------------------------
 
 END_NAMESPACE_DGL
+
+#endif