diff --git a/lang/occam/comp/code.c b/lang/occam/comp/code.c
index e6008bba3..ec4a8e8a7 100644
--- a/lang/occam/comp/code.c
+++ b/lang/occam/comp/code.c
@@ -3,7 +3,7 @@
  * (c) copyright 1987 by the Vrije Universiteit, Amsterdam, The Netherlands.
  * See the copyright notice in the ACK home directory, in the file "Copyright".
  */
-#include "em.h"
+#include "occam-em.h"
 #include "expr.h"
 #include "symtab.h"
 #include "sizes.h"
diff --git a/lang/occam/comp/em.h b/lang/occam/comp/occam-em.h
similarity index 92%
rename from lang/occam/comp/em.h
rename to lang/occam/comp/occam-em.h
index 73a27e4b2..33b0c7453 100644
--- a/lang/occam/comp/em.h
+++ b/lang/occam/comp/occam-em.h
@@ -13,6 +13,9 @@ int new_label(), new_dot_label();
 char *proc_label();
 extern char *curr_file;
 
+/* dtrg: hack to avoid clashing with the Posix exp() function. */
+#define exp myexp
+
 void cwv(), cvw();
 void bxx(), Loc(), Lol(), Lolp(), Lil(), Lof(), Lofp(), Lif();
 void Txx(), xxi(), Stl(), Inl(), Del(), Loe();