diff --git a/libraries/DataFlash/DataFlash.cpp b/libraries/DataFlash/DataFlash.cpp
index 1e095ab625..02b781ebb0 100644
--- a/libraries/DataFlash/DataFlash.cpp
+++ b/libraries/DataFlash/DataFlash.cpp
@@ -431,7 +431,7 @@ bool DataFlash_Class::logging_failed() const
 
 void DataFlash_Class::Log_Write_MessageF(const char *fmt, ...)
 {
-    char msg[64] {};
+    char msg[65] {}; // sizeof(log_Message.msg) + null-termination
 
     va_list ap;
     va_start(ap, fmt);
diff --git a/libraries/DataFlash/DataFlash_Backend.cpp b/libraries/DataFlash/DataFlash_Backend.cpp
index 1ddd48a711..691c5f8a3f 100644
--- a/libraries/DataFlash/DataFlash_Backend.cpp
+++ b/libraries/DataFlash/DataFlash_Backend.cpp
@@ -408,7 +408,7 @@ bool DataFlash_Backend::ShouldLog(bool is_critical)
 
 bool DataFlash_Backend::Log_Write_MessageF(const char *fmt, ...)
 {
-    char msg[64] {};
+    char msg[65] {}; // sizeof(log_Message.msg) + null-termination
 
     va_list ap;
     va_start(ap, fmt);