diff --git a/mex/sources/ms-sbvar/modify_for_mex.cc b/mex/sources/ms-sbvar/modify_for_mex.cc
index 2e32ae40a..52206e073 100644
--- a/mex/sources/ms-sbvar/modify_for_mex.cc
+++ b/mex/sources/ms-sbvar/modify_for_mex.cc
@@ -17,25 +17,12 @@
  * along with Dynare.  If not, see <https://www.gnu.org/licenses/>.
  */
 
-#if defined(MATLAB_MEX_FILE) || defined(OCTAVE_MEX_FILE)
+#include <dynmex.h>
 
-# include <dynmex.h>
-
-# ifdef __cplusplus
 extern "C"
+[[noreturn]]
+void
+msExit([[maybe_unused]] int status)
 {
-# endif
-
-  int constant_seed;
-
-  [[noreturn]]
-  void
-  msExit([[maybe_unused]] int status)
-  {
-    throw "Error in MS-SBVAR MEX file.\n";
-  }
-
-# ifdef __cplusplus
+  throw "Error in MS-SBVAR MEX file.\n";
 }
-# endif
-#endif
diff --git a/mex/sources/ms-sbvar/modify_for_mex.h b/mex/sources/ms-sbvar/modify_for_mex.h
index 973fa425f..3fcb78b4d 100644
--- a/mex/sources/ms-sbvar/modify_for_mex.h
+++ b/mex/sources/ms-sbvar/modify_for_mex.h
@@ -17,28 +17,34 @@
  * along with Dynare.  If not, see <https://www.gnu.org/licenses/>.
  */
 
-#ifndef _MEXMOD
-#define _MEXMOD
+#ifndef _MODIFY_FOR_MEX_H
+#define _MODIFY_FOR_MEX_H
 
-#if defined(MATLAB_MEX_FILE) || defined(OCTAVE_MEX_FILE)
+#include <dynmex.h>
+#include <dynblas.h>
+#include <dynlapack.h>
 
-# include <dynmex.h>
-# include <dynblas.h>
-# include <dynlapack.h>
-
-# define dw_malloc mxMalloc
-# define dw_calloc mxCalloc
-# define dw_realloc mxRealloc
-# define dw_free mxFree
-# define dw_exit msExit
+#define dw_malloc mxMalloc
+#define dw_calloc mxCalloc
+#define dw_realloc mxRealloc
+#define dw_free mxFree
+#define dw_exit msExit
 
 /* Handle Ctrl-C in Matlab/Octave */
-# ifdef MATLAB_MEX_FILE
-extern bool utIsInterruptPending();
+#ifdef MATLAB_MEX_FILE
+# ifdef __cplusplus
+extern "C"
 # else
-#  include <octave/quit.h>
+extern
 # endif
+bool utIsInterruptPending();
+#else
+# include <octave/quit.h>
+#endif
 
+#ifdef __cplusplus
+extern "C"
+#endif
 // NB: C23 has the [[noreturn]] attribute, so this #ifdef can be removed when
 // we upgrade
 #ifdef __cplusplus
@@ -48,7 +54,4 @@ _Noreturn
 #endif
 void msExit(int status);
 
-extern int constant_seed;
-
-#endif
-#endif
+#endif // _MODIFY_FOR_MEX_H