diff --git a/CHANGES b/CHANGES
index 669e737..5ddeb92 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,4 +1,16 @@
-The following are the changes from calc version 2.12.6.1 to date:
+The following are the changes from calc version 2.12.6.5 to date:
+
+    Fixed warning about undefined operations involving the qlink(q)
+    macro by deplacing that macro with an inline-function.  Thanks goes
+    to David Haller <dnh at opensuse dot org> for this fix.
+
+    NOTE for Windows 10 users: Pavel Nemec <pane at seznam dot cz>
+    reported that calc version 2.12.6.4 has been successfully
+    compiled, installed and running on Windows 10.  See README.WINDOWS
+    for more details.
+
+
+The following are the changes from calc version 2.12.6.1 to 2.12.6.3:
 
     Improved gen_v1(h,n) in lucas.cal to use an even faster search method.
 
diff --git a/Makefile.ship b/Makefile.ship
index 633a8c0..d7b972d 100644
--- a/Makefile.ship
+++ b/Makefile.ship
@@ -1054,7 +1054,7 @@ EXT=
 
 # The default calc versions
 #
-VERSION= 2.12.6.4
+VERSION= 2.12.6.5
 
 # Names of shared libraries with versions
 #
diff --git a/README.WINDOWS b/README.WINDOWS
index 99c15ed..13b6210 100644
--- a/README.WINDOWS
+++ b/README.WINDOWS
@@ -10,6 +10,21 @@ NOTE: The main developers do not have access to a Windoz based platform.
       Of course you are welcome to send us any patches that fix your
       Windoz build environment.
 
+
+=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
+=-= compiling with Windows Subsystem for Linux (WSL) =-Cygwin =-=
+=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
+
+It has been reported that calc version 2.12.6.4 has been successfully
+compiled, installed and running on Windows 10 on 2018 Jan 21.
+
+We were told:
+
+  "The Windows Subsystem for Linux (WSL) is a new Windows 10 feature that
+   enables you to run native Linux command-line tools directly on Windows"
+
+   https://docs.microsoft.com/cs-cz/windows/wsl/about
+
 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 =-= compiling with Cygwin =-=
 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=
diff --git a/custom/Makefile b/custom/Makefile
index 3064ef1..156b4e0 100644
--- a/custom/Makefile
+++ b/custom/Makefile
@@ -348,7 +348,7 @@ EXT=
 
 # The default calc versions
 #
-VERSION= 2.12.6.4
+VERSION= 2.12.6.5
 
 # Names of shared libraries with versions
 #
diff --git a/custom/Makefile.head b/custom/Makefile.head
index 3e6e783..4500487 100644
--- a/custom/Makefile.head
+++ b/custom/Makefile.head
@@ -348,7 +348,7 @@ EXT=
 
 # The default calc versions
 #
-VERSION= 2.12.6.4
+VERSION= 2.12.6.5
 
 # Names of shared libraries with versions
 #
diff --git a/qmath.h b/qmath.h
index 3444f51..45ae7ab 100644
--- a/qmath.h
+++ b/qmath.h
@@ -254,7 +254,9 @@ E_FUNC NUMBER *swap_HALF_in_NUMBER(NUMBER *dest, NUMBER *src, BOOL all);
 #define qhighbit(q)	(zhighbit((q)->num))
 #define qlowbit(q)	(zlowbit((q)->num))
 #define qdivcount(q1, q2)	(zdivcount((q1)->num, (q2)->num))
-#define qlink(q)	((q)->links++, (q))
+/* operation on #q may be undefined, so replace with an inline-function */
+/* was: #define qlink(q)	((q)->links++, (q)) */
+static inline NUMBER* qlink(NUMBER* q) { if(q) { (q)->links++; } return q; }
 
 #define qfree(q)	{if (--((q)->links) <= 0) qfreenum(q);}
 
diff --git a/version.c b/version.c
index 4ca99c4..90b0ccf 100644
--- a/version.c
+++ b/version.c
@@ -45,7 +45,7 @@ static char *program;
 #define MAJOR_VER	2	/* major library version */
 #define MINOR_VER	12	/* minor library version */
 #define MAJOR_PATCH	6	/* major software level under library version */
-#define MINOR_PATCH	4	/* minor software level or 0 if not patched */
+#define MINOR_PATCH	5	/* minor software level or 0 if not patched */
 
 
 /*