diff --git a/Eigen/src/Core/IO.h b/Eigen/src/Core/IO.h
index ca5f247ed..0a1b583d6 100644
--- a/Eigen/src/Core/IO.h
+++ b/Eigen/src/Core/IO.h
@@ -68,8 +68,8 @@ struct IOFormat {
     // TODO check if rowPrefix, rowSuffix or rowSeparator contains a newline
     // don't add rowSpacer if columns are not to be aligned
     if ((flags & DontAlignCols)) return;
-    int i = int(matSuffix.length()) - 1;
-    while (i >= 0 && matSuffix[i] != '\n') {
+    int i = int(matPrefix.length()) - 1;
+    while (i >= 0 && matPrefix[i] != '\n') {
       rowSpacer += ' ';
       i--;
     }