diff -Nru ginac-1.5.8.orig/ginac/ex.h ginac-1.5.8.hack/ginac/ex.h
--- ginac-1.5.8.orig/ginac/ex.h	2010-03-05 20:39:00 +0000
+++ ginac-1.5.8.hack/ginac/ex.h	2010-09-14 08:08:50 +0000
@@ -32,6 +32,11 @@
 #include <stack>
 
 namespace GiNaC {
+#ifdef _MSC_VER
+  // MSVC produces a different symbol for _ex0 when it is declared inside   
+  // ex::is_zero() than when it is declared at top level as follows
+  extern const ex _ex0;
+#endif
 
 /** Helper class to initialize the library.  There must be one static object
  *  of this class in every object file that makes use of our flyweights in
@@ -204,7 +209,12 @@
 	// comparison
 	int compare(const ex & other) const;
 	bool is_equal(const ex & other) const;
-	bool is_zero() const { extern const ex _ex0; return is_equal(_ex0); }
+	bool is_zero() const { 
+#ifndef _MSC_VER
+	  extern const ex _ex0;
+#endif
+	  return is_equal(_ex0); 
+	}
 	bool is_zero_matrix() const;
 	
 	// symmetry
diff -Nru ginac-1.5.8.orig/ginac/parser/parse_binop_rhs.cpp ginac-1.5.8.hack/ginac/parser/parse_binop_rhs.cpp
--- ginac-1.5.8.orig/ginac/parser/parse_binop_rhs.cpp	2010-03-05 20:39:00 +0000
+++ ginac-1.5.8.hack/ginac/parser/parse_binop_rhs.cpp	2010-09-14 08:06:23 +0000
@@ -114,7 +114,7 @@
 	}
 }
 
-extern numeric* _num_1_p;
+extern const numeric* _num_1_p;
 
 static ex make_minus_expr(const exvector& args)
 {
diff -Nru ginac-1.5.8.orig/ginac/parser/parser.cpp ginac-1.5.8.hack/ginac/parser/parser.cpp
--- ginac-1.5.8.orig/ginac/parser/parser.cpp	2010-07-06 12:39:14 +0000
+++ ginac-1.5.8.hack/ginac/parser/parser.cpp	2010-09-14 08:06:18 +0000
@@ -120,8 +120,7 @@
 	return e;
 }
 
-extern numeric* _num_1_p;
-extern ex _ex0;
+extern const ex _ex0;
 
 /// unary_expr: [+-] expression
 ex parser::parse_unary_expr()