diff --git a/configure b/configure
index 53edafab2b..371f62000e 100755
--- a/configure
+++ b/configure
@@ -706,8 +706,6 @@ DNSTAPSRCS
 DNSTAP
 FSTRM_CAPTURE
 PROTOC_C
-IRS_PLATFORM_USEDECLSPEC
-ISC_PLATFORM_USEDECLSPEC
 ISC_PLATFORM_HAVESYSUNH
 LIBCAP_LIBS
 DST_EXTRA_SRCS
@@ -17939,15 +17937,6 @@ $as_echo "#define HAVE_STAT_NSEC 1" >>confdefs.h
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
-#
-# Microsoft has their own way of handling shared libraries that requires
-# additional qualifiers on extern variables.  Unix systems don't need it.
-#
-
-ISC_PLATFORM_USEDECLSPEC="#undef ISC_PLATFORM_USEDECLSPEC"
-
-IRS_PLATFORM_USEDECLSPEC="#undef IRS_PLATFORM_USEDECLSPEC"
-
 #
 # Check for if_nametoindex() for IPv6 scoped addresses support
 #
diff --git a/configure.in b/configure.in
index 4c99a89561..ff783632f9 100644
--- a/configure.in
+++ b/configure.in
@@ -1999,15 +1999,6 @@ AC_COMPILE_IFELSE(
       ]])],
    [AC_DEFINE([HAVE_STAT_NSEC], [1], [define if struct stat has st_mtim.tv_nsec field])])
 
-#
-# Microsoft has their own way of handling shared libraries that requires
-# additional qualifiers on extern variables.  Unix systems don't need it.
-#
-AC_SUBST(ISC_PLATFORM_USEDECLSPEC)
-ISC_PLATFORM_USEDECLSPEC="#undef ISC_PLATFORM_USEDECLSPEC"
-AC_SUBST(IRS_PLATFORM_USEDECLSPEC)
-IRS_PLATFORM_USEDECLSPEC="#undef IRS_PLATFORM_USEDECLSPEC"
-
 #
 # Check for if_nametoindex() for IPv6 scoped addresses support
 #
diff --git a/lib/irs/include/irs/platform.h.in b/lib/irs/include/irs/platform.h.in
index 78c91ce144..5599374078 100644
--- a/lib/irs/include/irs/platform.h.in
+++ b/lib/irs/include/irs/platform.h.in
@@ -18,15 +18,7 @@
  ***** Platform-dependent defines.
  *****/
 
-#ifndef IRS_PLATFORM_USEDECLSPEC
 #define LIBIRS_EXTERNAL_DATA
-#else
-#ifdef LIBIRS_EXPORTS
-#define LIBIRS_EXTERNAL_DATA __declspec(dllexport)
-#else
-#define LIBIRS_EXTERNAL_DATA __declspec(dllimport)
-#endif
-#endif
 
 /*
  * Tell Emacs to use C mode on this file.
diff --git a/lib/irs/win32/include/irs/platform.h b/lib/irs/win32/include/irs/platform.h
index 78c91ce144..7170a73f07 100644
--- a/lib/irs/win32/include/irs/platform.h
+++ b/lib/irs/win32/include/irs/platform.h
@@ -18,15 +18,11 @@
  ***** Platform-dependent defines.
  *****/
 
-#ifndef IRS_PLATFORM_USEDECLSPEC
-#define LIBIRS_EXTERNAL_DATA
-#else
 #ifdef LIBIRS_EXPORTS
 #define LIBIRS_EXTERNAL_DATA __declspec(dllexport)
 #else
 #define LIBIRS_EXTERNAL_DATA __declspec(dllimport)
 #endif
-#endif
 
 /*
  * Tell Emacs to use C mode on this file.
diff --git a/lib/isc/include/isc/platform.h.in b/lib/isc/include/isc/platform.h.in
index dc8cc619b3..90b9a2ee36 100644
--- a/lib/isc/include/isc/platform.h.in
+++ b/lib/isc/include/isc/platform.h.in
@@ -32,10 +32,6 @@
 
 #define ISC_STRERRORSIZE 128
 
-/***
- *** Network.
- ***/
-
 /***
  *** Miscellaneous.
  ***/
@@ -58,11 +54,6 @@
  */
 @ISC_PLATFORM_KRB5HEADER@
 
-/*
- * Used to control how extern data is linked; needed for Win32 platforms.
- */
-@ISC_PLATFORM_USEDECLSPEC@
-
 /*
  * Define if the platform has <sys/un.h>.
  */
@@ -78,7 +69,6 @@
  ***	Windows dll support.
  ***/
 
-#ifndef ISC_PLATFORM_USEDECLSPEC
 #define LIBISC_EXTERNAL_DATA
 #define LIBDNS_EXTERNAL_DATA
 #define LIBISCCC_EXTERNAL_DATA
@@ -86,43 +76,6 @@
 #define LIBNS_EXTERNAL_DATA
 #define LIBBIND9_EXTERNAL_DATA
 #define LIBTESTS_EXTERNAL_DATA
-#else /*! \brief ISC_PLATFORM_USEDECLSPEC */
-#ifdef LIBISC_EXPORTS
-#define LIBISC_EXTERNAL_DATA __declspec(dllexport)
-#else
-#define LIBISC_EXTERNAL_DATA __declspec(dllimport)
-#endif
-#ifdef LIBDNS_EXPORTS
-#define LIBDNS_EXTERNAL_DATA __declspec(dllexport)
-#else
-#define LIBDNS_EXTERNAL_DATA __declspec(dllimport)
-#endif
-#ifdef LIBISCCC_EXPORTS
-#define LIBISCCC_EXTERNAL_DATA __declspec(dllexport)
-#else
-#define LIBISCCC_EXTERNAL_DATA __declspec(dllimport)
-#endif
-#ifdef LIBISCCFG_EXPORTS
-#define LIBISCCFG_EXTERNAL_DATA __declspec(dllexport)
-#else
-#define LIBISCCFG_EXTERNAL_DATA __declspec(dllimport)
-#endif
-#ifdef LIBNS_EXPORTS
-#define LIBNS_EXTERNAL_DATA __declspec(dllexport)
-#else
-#define LIBNS_EXTERNAL_DATA __declspec(dllimport)
-#endif
-#ifdef LIBBIND9_EXPORTS
-#define LIBBIND9_EXTERNAL_DATA __declspec(dllexport)
-#else
-#define LIBBIND9_EXTERNAL_DATA __declspec(dllimport)
-#endif
-#ifdef LIBTESTS_EXPORTS
-#define LIBTESTS_EXTERNAL_DATA __declspec(dllexport)
-#else
-#define LIBTESTS_EXTERNAL_DATA __declspec(dllimport)
-#endif
-#endif /*! \brief ISC_PLATFORM_USEDECLSPEC */
 
 /*
  * Tell emacs to use C mode for this file.
diff --git a/lib/isc/win32/include/isc/platform.h.in b/lib/isc/win32/include/isc/platform.h.in
index 1e0a0354dc..3ae3e3c895 100644
--- a/lib/isc/win32/include/isc/platform.h.in
+++ b/lib/isc/win32/include/isc/platform.h.in
@@ -46,11 +46,6 @@
 
 #undef MSG_TRUNC
 
-/*
- * Used to control how extern data is linked; needed for Win32 platforms.
- */
-#define ISC_PLATFORM_USEDECLSPEC 1
-
 /*
  * Define if the platform has <sys/un.h>.
  */