diff --git a/prism/src/mtbdd/PM_ExportVector.cc b/prism/src/mtbdd/PM_ExportVector.cc
index c1726f72..0f145497 100644
--- a/prism/src/mtbdd/PM_ExportVector.cc
+++ b/prism/src/mtbdd/PM_ExportVector.cc
@@ -26,6 +26,7 @@
 
 // includes
 #include "PrismMTBDD.h"
+#include <cinttypes>
 #include <util.h>
 #include <cudd.h>
 #include <dd.h>
@@ -36,7 +37,7 @@
 //------------------------------------------------------------------------------
 
 // local function prototypes
-static void export_rec(DdNode *dd, DdNode **vars, int num_vars, int level, ODDNode *odd, long index);
+static void export_rec(DdNode *dd, DdNode **vars, int num_vars, int level, ODDNode *odd, int64_t index);
 
 // globals
 static const char *export_name;
@@ -82,7 +83,7 @@ jstring fn		// filename
 
 //------------------------------------------------------------------------------
 
-static void export_rec(DdNode *dd, DdNode **vars, int num_vars, int level, ODDNode *odd, long index)
+static void export_rec(DdNode *dd, DdNode **vars, int num_vars, int level, ODDNode *odd, int64_t index)
 {
 	DdNode *e, *t;
 	
@@ -92,9 +93,9 @@ static void export_rec(DdNode *dd, DdNode **vars, int num_vars, int level, ODDNo
 	// base case - non zero terminal
 	if (level == num_vars) {
 		switch (export_type) {
-		case EXPORT_PLAIN: export_string("%d %.12g\n", index, Cudd_V(dd)); break;
-		case EXPORT_MATLAB: export_string("%s(%d)=%.12g;\n", export_name, index+1, Cudd_V(dd)); break;
-		case EXPORT_MRMC: export_string("%d %.12g\n", index+1, Cudd_V(dd)); break;
+		case EXPORT_PLAIN: export_string("%" PRId64 " %.12g\n", index, Cudd_V(dd)); break;
+		case EXPORT_MATLAB: export_string("%s(%" PRId64 ")=%.12g;\n", export_name, index+1, Cudd_V(dd)); break;
+		case EXPORT_MRMC: export_string("%" PRId64 " %.12g\n", index+1, Cudd_V(dd)); break;
 		}
 		return;
 	}