diff --git a/libvips/foreign/matrixload.c b/libvips/foreign/matrixload.c
index 5cec716d..5bc6f442 100644
--- a/libvips/foreign/matrixload.c
+++ b/libvips/foreign/matrixload.c
@@ -422,7 +422,7 @@ static int
 vips_foreign_load_matrix_source_is_a_source( VipsSource *source )
 {
 	unsigned char *data;
-	size_t bytes_read;
+	gint64 bytes_read;
 	char line[80];
 	int width;
 	int height;
diff --git a/libvips/foreign/svgload.c b/libvips/foreign/svgload.c
index 4b86980b..b39a7a7e 100644
--- a/libvips/foreign/svgload.c
+++ b/libvips/foreign/svgload.c
@@ -664,7 +664,7 @@ gboolean
 vips_foreign_load_svg_source_is_a_source( VipsSource *source )
 {
 	unsigned char *data;
-	size_t bytes_read;
+	gint64 bytes_read;
 
 	if( (bytes_read = vips_source_sniff_at_most( source, 
 		&data, SVG_HEADER_SIZE )) <= 0 )