diff --git a/Tools/ardupilotwaf/embed.py b/Tools/ardupilotwaf/embed.py
index de7e77a483..1ca4c8f996 100755
--- a/Tools/ardupilotwaf/embed.py
+++ b/Tools/ardupilotwaf/embed.py
@@ -32,17 +32,21 @@ def embed_file(out, f, idx, embedded_name, uncompressed):
     write_encode(out, '__EXTFLASHFUNC__ static const uint8_t ap_romfs_%u[] = {' % idx)
 
     if uncompressed:
-        # ensure nul termination
-        if contents[-1] != 0:
-            contents += bytes([0])
+        # terminate if there's not already an existing null. we don't add it to
+        # the contents to avoid storing the wrong length
+        null_terminate = 0 not in contents
         b = contents
     else:
         # compress it (max level, max window size, raw stream, max mem usage)
         z = zlib.compressobj(level=9, method=zlib.DEFLATED, wbits=-15, memLevel=9)
         b = z.compress(contents)
         b += z.flush()
+        # decompressed data will be null terminated at runtime, nothing to do here
+        null_terminate = False
 
     write_encode(out, ",".join(str(c) for c in b))
+    if null_terminate:
+        write_encode(out, ",0")
     write_encode(out, '};\n\n');
     return crc, len(contents)
 
diff --git a/libraries/AP_ROMFS/AP_ROMFS.cpp b/libraries/AP_ROMFS/AP_ROMFS.cpp
index a7e63dab49..67adb2313c 100644
--- a/libraries/AP_ROMFS/AP_ROMFS.cpp
+++ b/libraries/AP_ROMFS/AP_ROMFS.cpp
@@ -45,10 +45,10 @@ const AP_ROMFS::embedded_file *AP_ROMFS::find_file(const char *name)
 }
 
 /*
-  find a compressed file and uncompress it. Space for decompressed
-  data comes from malloc. Caller must be careful to free the resulting
-  data after use. The next byte after the file data is guaranteed to
-  be null
+  find a compressed file and uncompress it. Space for decompressed data comes
+  from malloc. Caller must be careful to free the resulting data after use. The
+  file data buffer is guaranteed to contain at least one null (though it may be
+  at buf[size]).
 */
 const uint8_t *AP_ROMFS::find_decompress(const char *name, uint32_t &size)
 {
@@ -58,7 +58,7 @@ const uint8_t *AP_ROMFS::find_decompress(const char *name, uint32_t &size)
     }
 
 #ifdef HAL_ROMFS_UNCOMPRESSED
-    size = f->compressed_size;
+    size = f->decompressed_size;
     return f->contents;
 #else
     uint8_t *decompressed_data = (uint8_t *)malloc(f->decompressed_size+1);
@@ -66,7 +66,7 @@ const uint8_t *AP_ROMFS::find_decompress(const char *name, uint32_t &size)
         return nullptr;
     }
 
-    // explicitly null terimnate the data
+    // explicitly null-terminate the data
     decompressed_data[f->decompressed_size] = 0;
 
     TINF_DATA *d = (TINF_DATA *)malloc(sizeof(TINF_DATA));