diff --git a/src/tools/clu_base64.c b/src/tools/clu_base64.c
index 6667ee5a..648a233d 100644
--- a/src/tools/clu_base64.c
+++ b/src/tools/clu_base64.c
@@ -199,7 +199,7 @@ int wolfCLU_Base64Setup(int argc, char** argv)
         else {
             /* For regular base64 decoding */
             /* Calculate output size */
-            outputSz = (inputSz * 3) / 4 + 1;
+            outputSz = (inputSz / 4) * 3 + (inputSz % 4) * 3 / 4 + 1;
 
             /* Allocate output buffer */
             output = (byte*)XMALLOC(outputSz, HEAP_HINT,