diff --git a/src/ModelMap.cxx b/src/ModelMap.cxx
index 5e08c6891..df295d207 100644
--- a/src/ModelMap.cxx
+++ b/src/ModelMap.cxx
@@ -14,6 +14,7 @@
 #include "tip/IFileSvc.h"
 #include "tip/Image.h"
 #include "tip/Table.h"
+#include "tip/Header.h"
 
 #include "st_facilities/FitsUtil.h"
 
@@ -174,8 +175,16 @@ void ModelMap::writeOutputMap_wcs(const std::string & outfile,
      if ( itr->getName().find("NAXIS") != std::string::npos ) {
        continue;
      }
-     output_header.append(*itr);
+     // append any new keywords and any new HISTORY or COMMENT keywords (some of these might end up duplicated)
+     // or update the value for any existing kewords. - TS 03/21/25  
+     auto kwItr = output_header.find(itr->getName());
+     if (kwItr == output_header.end() || "COMMENT" == kwItr->getName() || "HISTORY" == kwItr->getName()){
+       output_header.append(*itr);
+     } else {
+       kwItr->setValue(itr->getValue());
+     }
    }
+
    if (outtype == "CMAP") {
      output_header.erase("CTYPE3");
      output_header.erase("CRPIX3");