diff --git a/libraries/DataFlash/DataFlash_Backend.h b/libraries/DataFlash/DataFlash_Backend.h
index 308049479d..815ab184c8 100644
--- a/libraries/DataFlash/DataFlash_Backend.h
+++ b/libraries/DataFlash/DataFlash_Backend.h
@@ -60,7 +60,7 @@ public:
 
     void set_mission(const AP_Mission *mission);
 
-    virtual uint16_t bufferspace_available() = 0;
+    virtual uint32_t bufferspace_available() = 0;
 
     virtual uint16_t start_new_log(void) = 0;
     bool log_write_started;
diff --git a/libraries/DataFlash/DataFlash_Block.cpp b/libraries/DataFlash/DataFlash_Block.cpp
index e8a011f68b..41397282c3 100644
--- a/libraries/DataFlash/DataFlash_Block.cpp
+++ b/libraries/DataFlash/DataFlash_Block.cpp
@@ -12,11 +12,11 @@ extern AP_HAL::HAL& hal;
 // this if (and only if!) the low level format changes
 #define DF_LOGGING_FORMAT    0x28122013
 
-uint16_t DataFlash_Block::bufferspace_available()
+uint32_t DataFlash_Block::bufferspace_available()
 {
     // because DataFlash_Block devices are ring buffers, we *always*
     // have room...
-    return df_NumPages * df_PageSize; 
+    return df_NumPages * df_PageSize;
 }
 
 // *** DATAFLASH PUBLIC FUNCTIONS ***
diff --git a/libraries/DataFlash/DataFlash_Block.h b/libraries/DataFlash/DataFlash_Block.h
index e5ca25a0d0..e77a8b6d49 100644
--- a/libraries/DataFlash/DataFlash_Block.h
+++ b/libraries/DataFlash/DataFlash_Block.h
@@ -40,7 +40,7 @@ public:
     void ShowDeviceInfo(AP_HAL::BetterStream *port);
     void ListAvailableLogs(AP_HAL::BetterStream *port);
 
-    uint16_t bufferspace_available();
+    uint32_t bufferspace_available();
 
 private:
     struct PageHeader {
diff --git a/libraries/DataFlash/DataFlash_File.cpp b/libraries/DataFlash/DataFlash_File.cpp
index 462a8765a2..0ba0a74670 100644
--- a/libraries/DataFlash/DataFlash_File.cpp
+++ b/libraries/DataFlash/DataFlash_File.cpp
@@ -473,7 +473,7 @@ bool DataFlash_File::WritePrioritisedBlock(const void *pBuffer, uint16_t size, b
         return false;
     }
         
-    uint16_t space = _writebuf.space();
+    uint32_t space = _writebuf.space();
 
     if (_writing_startup_messages &&
         _startup_messagewriter->fmt_done()) {
diff --git a/libraries/DataFlash/DataFlash_File.h b/libraries/DataFlash/DataFlash_File.h
index b44848bc69..8ca1061433 100644
--- a/libraries/DataFlash/DataFlash_File.h
+++ b/libraries/DataFlash/DataFlash_File.h
@@ -44,7 +44,7 @@ public:
 
     /* Write a block of data at current offset */
     bool WritePrioritisedBlock(const void *pBuffer, uint16_t size, bool is_critical);
-    uint16_t bufferspace_available();
+    uint32_t bufferspace_available();
 
     // high level interface
     uint16_t find_last_log() override;
@@ -129,9 +129,9 @@ private:
         }
         return ret;
     };
-    uint16_t non_messagewriter_message_reserved_space() const {
+    uint32_t non_messagewriter_message_reserved_space() const {
         // possibly make this a proportional to buffer size?
-        uint16_t ret = 1024;
+        uint32_t ret = 1024;
         if (ret >= _writebuf.get_size()) {
             // need to allow messages out from the messagewriters.  In
             // this case while you have a messagewriter you won't get
diff --git a/libraries/DataFlash/DataFlash_MAVLink.cpp b/libraries/DataFlash/DataFlash_MAVLink.cpp
index 2f7b7ea8c7..8b258ee50c 100644
--- a/libraries/DataFlash/DataFlash_MAVLink.cpp
+++ b/libraries/DataFlash/DataFlash_MAVLink.cpp
@@ -55,7 +55,7 @@ bool DataFlash_MAVLink::logging_failed() const
     return !_sending_to_client;
 }
 
-uint16_t DataFlash_MAVLink::bufferspace_available() {
+uint32_t DataFlash_MAVLink::bufferspace_available() {
     return (_blockcount_free * 200 + remaining_space_in_current_block());
 }
 
diff --git a/libraries/DataFlash/DataFlash_MAVLink.h b/libraries/DataFlash/DataFlash_MAVLink.h
index 967ef818fe..2beb241ca1 100644
--- a/libraries/DataFlash/DataFlash_MAVLink.h
+++ b/libraries/DataFlash/DataFlash_MAVLink.h
@@ -157,7 +157,7 @@ private:
     void Log_Write_DF_MAV(DataFlash_MAVLink &df);
     
     void internal_error();
-    uint16_t bufferspace_available() override; // in bytes
+    uint32_t bufferspace_available() override; // in bytes
     uint8_t remaining_space_in_current_block();
     // write buffer
     uint8_t _blockcount_free;