diff --git a/fitparse/base.py b/fitparse/base.py
index ccecd87..a2433c2 100644
--- a/fitparse/base.py
+++ b/fitparse/base.py
@@ -71,7 +71,7 @@ def _read(self, size):
         return data
 
     def _read_struct(self, fmt, endian='<', data=None, always_tuple=False):
-        fmt_with_endian = "%s%s" % (endian, fmt)
+        fmt_with_endian = endian + fmt
         size = struct.calcsize(fmt_with_endian)
         if size <= 0:
             raise FitParseError("Invalid struct format: %s" % fmt_with_endian)
@@ -251,10 +251,7 @@ def _parse_raw_values_from_data_message(self, def_mesg):
             base_type = field_def.base_type
             is_byte = base_type.name == 'byte'
             # Struct to read n base types (field def size / base type size)
-            struct_fmt = '%d%s' % (
-                field_def.size / base_type.size,
-                base_type.fmt,
-            )
+            struct_fmt = str(int(field_def.size / base_type.size)) + base_type.fmt
 
             # Extract the raw value, ask for a tuple if it's a byte type
             raw_value = self._read_struct(