diff --git a/py/lexer.c b/py/lexer.c
index abc1f3e..6e5cc18 100644
--- a/py/lexer.c
+++ b/py/lexer.c
@@ -672,7 +672,7 @@
     lex->source_name = src_name;
     lex->reader = reader;
     lex->line = 1;
-    lex->column = -2;   // account for 3 dummy bytes
+    lex->column = (size_t)-2; // account for 3 dummy bytes
     lex->emit_dent = 0;
     lex->nested_bracket_level = 0;
     lex->alloc_indent_level = MICROPY_ALLOC_LEXER_INDENT_INIT;