diff --git a/libuavcan/include/uavcan/marshal/char_array_formatter.hpp b/libuavcan/include/uavcan/marshal/char_array_formatter.hpp
index 76c3948ad0..e805f162a4 100644
--- a/libuavcan/include/uavcan/marshal/char_array_formatter.hpp
+++ b/libuavcan/include/uavcan/marshal/char_array_formatter.hpp
@@ -85,11 +85,15 @@ public:
     {
         while (s && *s)
         {
-            if (*s == '%' && *++s != '%')
+            if (*s == '%')
             {
-                writeValue(value);
-                write(++s, args...);
-                break;
+                s += 1;
+                if (*s != '%')
+                {
+                    writeValue(value);
+                    write(++s, args...);
+                    break;
+                }
             }
             writeValue(*s++);
         }