diff --git a/src/core/codestream/ojph_params_local.h b/src/core/codestream/ojph_params_local.h
index 9c169d6..bac0c35 100644
--- a/src/core/codestream/ojph_params_local.h
+++ b/src/core/codestream/ojph_params_local.h
@@ -192,7 +192,7 @@ namespace ojph {
       void check_validity()
       {
         if (XTsiz == 0 && YTsiz == 0)
-        { XTsiz = Xsiz - XOsiz; YTsiz = Ysiz - YOsiz; }
+        { XTsiz = Xsiz + XOsiz; YTsiz = Ysiz + YOsiz; }
         if (Xsiz == 0 || Ysiz == 0 || XTsiz == 0 || YTsiz == 0)
           OJPH_ERROR(0x00040001, 
             "You cannot set image extent nor tile size to zero");
diff --git a/tests/test_executables.cpp b/tests/test_executables.cpp
index 908e6ce..50e8f6d 100644
--- a/tests/test_executables.cpp
+++ b/tests/test_executables.cpp
@@ -1220,8 +1220,8 @@ TEST(TestExecutables, SimpleEncIrv97TallNarrow) {
 // The compressed file is obtained using these command-line options:
 // -o simple_enc_irv97_tall_narrow1.j2c -image_offset {1,0} -qstep 0.1
 TEST(TestExecutables, SimpleEncIrv97TallNarrow1) {
-  double mse[3] = { 96.7935, 69.6824, 66.7822};
-  int pae[3] = { 41, 39, 35};
+  double mse[3] = { 100.905762, 76.113037, 72.834717};
+  int pae[3] = { 39, 35, 34};
   run_ojph_compress("tall_narrow.ppm",
                     "simple_enc_irv97_tall_narrow1", "", "j2c",
                     "-image_offset \"{1,0}\" -qstep 0.1");