diff --git a/choices.h b/choices.h
index 2b74d86..0b0be82 100644
--- a/choices.h
+++ b/choices.h
@@ -1,6 +1,7 @@
 /*! \file ko.h
  \brief default choices
 */
+#pragma once
 
 #define RESTARTGENERALINDICES
 
diff --git a/ko.h b/ko.h
index d962733..1673f1e 100644
--- a/ko.h
+++ b/ko.h
@@ -1,6 +1,7 @@
 /*! \file ko.h
  \brief constants, variables, and function definitions
 */
+#pragma once
 
 //small and big numbers
 #define SMALL 1.e-80 
diff --git a/mdefs.h b/mdefs.h
index f42080a..2e9a571 100644
--- a/mdefs.h
+++ b/mdefs.h
@@ -6,6 +6,7 @@
 
 
 *************************************************************************/
+#pragma once
 
 /* C language definitions for use with Mathematica output */
 
diff --git a/mnemonics.h b/mnemonics.h
index ec4480d..41205c7 100644
--- a/mnemonics.h
+++ b/mnemonics.h
@@ -1,6 +1,7 @@
 /*! \file ko.h
  \brief mnemonics for various indices
 */
+#pragma once
 
 //rad or hydro
 #define RAD 1
diff --git a/problem.h b/problem.h
index 4d1edbb..bce2c54 100644
--- a/problem.h
+++ b/problem.h
@@ -1,5 +1,6 @@
 //KORAL - problem.h
 //choice of the problem plus some definitions
+#pragma once
 
 //available problems: