diff --git a/CHANGELOG.txt b/CHANGELOG.txt
index 741a787..281f965 100644
--- a/CHANGELOG.txt
+++ b/CHANGELOG.txt
@@ -4,4 +4,5 @@ Current:
     - REMOVE: Removed setUTM()
     - NEW: warp() options:
         - useUTM - build output raster in UTM projection
-        - zerosAsND - set no data value to zero
\ No newline at end of file
+        - zerosAsND - set no data value to zero
+    - FIX: calculation of UTM zone number
diff --git a/src/msuproj-cli.cpp b/src/msuproj-cli.cpp
index 751f151..88ff796 100644
--- a/src/msuproj-cli.cpp
+++ b/src/msuproj-cli.cpp
@@ -62,14 +62,11 @@ int main(int argc, char *argv[])
 
     if (srcFile.empty() || gcpFile.empty())
     {
-        printf("ERROR: input and output not specified\n"
+        printf("ERROR: input files are not specified\n"
                "print \"-h\" for help\n");
         return 1;
     }
 
-    if (dstFile.empty())
-        dstFile = srcFile + string(".tif");
-
     retCode code;
 
     code = msuObj.setSRC(srcFile.c_str());
@@ -86,6 +83,14 @@ int main(int argc, char *argv[])
         return code;
     }
 
+    if (dstFile.empty())
+    {
+        dstFile = srcFile;
+        if (useUTM)
+            dstFile += "_" + string(msuObj.getUTM());
+        dstFile += ".tif";
+    }
+
     msuObj.setDST(dstFile.c_str());
 
     printf("Processing warp operation");
diff --git a/src/msuproj.cpp b/src/msuproj.cpp
index 30074ea..5e88781 100644
--- a/src/msuproj.cpp
+++ b/src/msuproj.cpp
@@ -112,8 +112,10 @@ const msumr::retCode msumr::msugeo::readGCP(const char *file)
     gcpXStep = srcXSize / gcpXSize + 1;
     gcpYStep = srcYSize / gcpYSize + 1;
 
-    zone = (int)((gcps[(int)(gcpSize / 2)].lon + 180) / 6) + 1;
-    hemisphere = (gcps[(int)(gcpSize / 2)].lat > 0);
+    zone = ((int)(((gcps[0].lon + gcps[gcpXSize - 1].lon +
+           gcps[gcpSize - gcpXSize].lon + gcps[gcpSize - 1].lon) / 4 + 180) / 6) + 1);
+    hemisphere = ((gcps[0].lat + gcps[gcpXSize - 1].lat +
+           gcps[gcpSize - gcpXSize].lat + gcps[gcpSize - 1].lat) / 4 > 0);
 
     return success;
 }