diff --git a/include/gfx/main.hpp b/include/gfx/main.hpp
index ad8bd4e4..73063c1c 100644
--- a/include/gfx/main.hpp
+++ b/include/gfx/main.hpp
@@ -21,7 +21,7 @@
 #include "gfx/rgba.hpp"
 
 struct Options {
-	uint16_t reversedWidth = 0; // -r, in pixels
+	uint16_t reversedWidth = 0; // -r, in tiles
 	bool reverse() const { return reversedWidth != 0; }
 
 	bool useColorCurve = false; // -C
diff --git a/src/gfx/reverse.cpp b/src/gfx/reverse.cpp
index 40e4b5ae..0a52fbb0 100644
--- a/src/gfx/reverse.cpp
+++ b/src/gfx/reverse.cpp
@@ -122,6 +122,9 @@ void reverse() {
 		options.verbosePrint(Options::VERB_INTERM, "Read %zu tilemap entries.\n", nbTileInstances);
 	}
 
+	if (nbTileInstances == 0) {
+		fatal("Cannot generate empty image");
+	}
 	if (nbTileInstances > options.maxNbTiles[0] + options.maxNbTiles[1]) {
 		warning("Read %zu tiles, more than the limit of %zu + %zu", nbTileInstances,
 		        options.maxNbTiles[0], options.maxNbTiles[1]);