diff --git a/stim/math/matrix.h b/stim/math/matrix.h
index 01f20e6..8f6e080 100644
--- a/stim/math/matrix.h
+++ b/stim/math/matrix.h
@@ -189,9 +189,9 @@ public:
 
 	std::string csv() {
 		std::stringstream csvss;
-		for (size_t i = 0; i < B; i++) {
+		for (size_t i = 0; i < R; i++) {
 			csvss << M[i];
-			for (size_t j = 0; j < B; j++) csvss << ", " << M[j * B + i];
+			for (size_t j = 0; j < C; j++) csvss << ", " << M[j * R + i];
 			csvss << std::endl;
 		}
 		return csvss.str();
--
libgit2 0.21.4