diff --git a/libs/pbd/msvc/msvc_pbd.cc b/libs/pbd/msvc/msvc_pbd.cc
index ddef968569..ab79d8f45d 100644
--- a/libs/pbd/msvc/msvc_pbd.cc
+++ b/libs/pbd/msvc/msvc_pbd.cc
@@ -262,6 +262,25 @@ trunc(double x)
 	return (floor(x));
 }
 
+//***************************************************************
+//
+//	log2()
+//
+// Emulates C99 log2() using log().
+//
+//	Returns:
+//
+//    On Success: The binary (base-2) logarithm of 'x'
+//                (e.g. log2(1024) == 10).
+//    On Failure: None, except that calling log(x) should generate
+//                an appropriate error for us (such as ERANGE etc).
+//
+LIBPBD_API double PBD_APICALLTYPE
+log2(double x)
+{
+	return (log(x) / log((double)2.0));
+}
+
 namespace PBD {
 
 //***************************************************************
diff --git a/libs/pbd/pbd/msvc_pbd.h b/libs/pbd/pbd/msvc_pbd.h
index bee9b8b4a4..7529619f1d 100644
--- a/libs/pbd/pbd/msvc_pbd.h
+++ b/libs/pbd/pbd/msvc_pbd.h
@@ -232,6 +232,7 @@ LIBPBD_API ssize_t			PBD_APICALLTYPE pwrite(int handle, const void *buf, size_t
 LIBPBD_API int				PBD_APICALLTYPE poll(struct pollfd *fds, nfds_t nfds, int timeout);
 LIBPBD_API double			PBD_APICALLTYPE round(double x);
 LIBPBD_API double			PBD_APICALLTYPE trunc(double x);
+LIBPBD_API double			PBD_APICALLTYPE log2(double x);
 
 namespace PBD {
 
diff --git a/msvc_extra_headers/ardourext/misc.h.input b/msvc_extra_headers/ardourext/misc.h.input
index 3ea4a806e9..5da7c41564 100644
--- a/msvc_extra_headers/ardourext/misc.h.input
+++ b/msvc_extra_headers/ardourext/misc.h.input
@@ -254,6 +254,10 @@ inline int64_t abs(int64_t val) throw()
 #define rint(value)  round(value)
 #if !defined(LIBPBD_API) || defined(PBD_IS_IN_WIN_STATIC_LIB)
 extern  double round(double x);
+
+// log2().... MSVC doesn't offer the C99 function 'log2()'
+// so let's emulate it.
+extern  double log2(double x);
 #endif
 
 #endif /* __ardour_msvc_extensions_h__ */