diff --git a/generic/tclStubInit.c b/generic/tclStubInit.c
index d3f6969..2c7ad8d 100644
--- a/generic/tclStubInit.c
+++ b/generic/tclStubInit.c
@@ -10,7 +10,7 @@
  */
 
 #include "tclInt.h"
-#include "tommath_private.h"
+#define MP_MIN(x, y) (((x) < (y)) ? (x) : (y))
 #include "tclTomMath.h"
 
 #ifdef __CYGWIN__
diff --git a/generic/tclZipfs.c b/generic/tclZipfs.c
index aa43e3d..31dbafc 100644
--- a/generic/tclZipfs.c
+++ b/generic/tclZipfs.c
@@ -76,10 +76,8 @@
 	}								\
     } while (0)
 
-#include "zlib.h"
-#include "crypt.h"
-#include "zutil.h"
-#include "crc32.h"
+#include <zlib.h>
+#include <minizip/crypt.h>
 
 static const z_crc_t* crc32tab;
 
diff --git a/pkgs/sqlite3.51.0/Makefile.in b/pkgs/sqlite3.51.0/Makefile.in
index 20ab0fd..3f650e4 100644
--- a/pkgs/sqlite3.51.0/Makefile.in
+++ b/pkgs/sqlite3.51.0/Makefile.in
@@ -148,7 +148,7 @@ SHARED_BUILD	= @SHARED_BUILD@
 INCLUDES	= @PKG_INCLUDES@ @TCL_INCLUDES@ -I. -I$(srcdir)/..
 #INCLUDES	= @PKG_INCLUDES@ @TCL_INCLUDES@ @TK_INCLUDES@ @TK_XINCLUDES@
 
-PKG_CFLAGS	= @PKG_CFLAGS@ -DSQLITE_EXTERN=
+PKG_CFLAGS	= @PKG_CFLAGS@
 
 # TCL_DEFS is not strictly need here, but if you remove it, then you
 # must make sure that configure.ac checks for the necessary components
diff --git a/pkgs/sqlite3.51.0/configure b/pkgs/sqlite3.51.0/configure
index e8bf713..c8299a6 100755
--- a/pkgs/sqlite3.51.0/configure
+++ b/pkgs/sqlite3.51.0/configure
@@ -601,8 +601,9 @@ MAKEFLAGS=
 # Identity of this package.
 PACKAGE_NAME='sqlite'
 PACKAGE_TARNAME='sqlite'
-PACKAGE_VERSION='3.51.0'
-PACKAGE_STRING='sqlite 3.51.0'
+printf "%s\n" "Using ${PKG_CONFIG} for sqlite3" >&6
+PACKAGE_VERSION="$(${PKG_CONFIG} --modversion sqlite3)"
+PACKAGE_STRING="sqlite $PACKAGE_VERSION"
 PACKAGE_BUGREPORT=''
 PACKAGE_URL=''
 
@@ -5736,6 +5737,7 @@ else case e in #(
 esac
 fi
 
+CFLAGS="$CFLAGS $(${PKG_CONFIG} --cflags sqlite3)"
 if test x$with_system_sqlite != xno; then
  ac_fn_c_check_header_compile "$LINENO" "sqlite3.h" "ac_cv_header_sqlite3_h" "$ac_includes_default"
 if test "x$ac_cv_header_sqlite3_h" = xyes
@@ -5747,7 +5749,7 @@ then :
   printf %s "(cached) " >&6
 else case e in #(
   e) ac_check_lib_save_LIBS=$LIBS
-LIBS="-lsqlite3  $LIBS"
+LIBS="$(${PKG_CONFIG} --libs sqlite3) $LIBS"
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -5787,7 +5789,7 @@ if test "x$ac_cv_lib_sqlite3_sqlite3_initialize" = xyes
 then :
   printf "%s\n" "#define USE_SYSTEM_SQLITE 1" >>confdefs.h
 
-      LIBS="$LIBS -lsqlite3"
+      LIBS="$LIBS $(${PKG_CONFIG:pkg-config} --libs sqlite3)"
 fi
 
 fi
diff --git a/pkgs/thread3.0.4/Makefile.in b/pkgs/thread3.0.4/Makefile.in
index 5bdae04..33f6536 100644
--- a/pkgs/thread3.0.4/Makefile.in
+++ b/pkgs/thread3.0.4/Makefile.in
@@ -152,7 +152,7 @@ PKG_ENV		= TCL_THREAD_LIBRARY=`@CYGPATH@ $(srcdir)/lib` \
 		  TCLLIBPATH="$(TCLLIBPATH) $(top_builddir)/../lib"
 
 TCLSH_PROG	= @TCLSH_PROG@
-TCLSH		= $(TCLSH_ENV) $(PKG_ENV) $(TCLSH_PROG)
+TCLSH		= $(TCLSH_ENV) $(PKG_ENV) $${HOST_TCLSH:-$(TCLSH_PROG)}
 
 #WISH_ENV	= TK_LIBRARY=`@CYGPATH@ $(TK_SRC_DIR)/library`
 #WISH_PROG	= @WISH_PROG@
diff --git a/unix/Makefile.in b/unix/Makefile.in
index 53f7c28..6b7f739 100644
--- a/unix/Makefile.in
+++ b/unix/Makefile.in
@@ -1,3 +1,5 @@
+PKG_CONFIG = @PKG_CONFIG@
+PKG_CONFIG_PATH = @PKG_CONFIG_PATH@
 #
 # This file is a Makefile for Tcl. If it has the name "Makefile.in" then it is
 # a template for a Makefile; to generate the actual Makefile, run
diff --git a/unix/configure.ac b/unix/configure.ac
index 80d676d..5eff9a2 100644
--- a/unix/configure.ac
+++ b/unix/configure.ac
@@ -158,10 +158,11 @@ AC_CHECK_HEADER([zlib.h],[
   AC_CHECK_TYPE([gz_header],[],[zlib_ok=no],[#include <zlib.h>])],[
   zlib_ok=no])
 AS_IF([test $zlib_ok = yes], [
-  AC_SEARCH_LIBS([deflateSetHeader],[z],[],[
+  AC_SEARCH_LIBS([deflateSetHeader],[z zs zlib zd zsd zlibd],[],[
     zlib_ok=no
   ])])
 AS_IF([test $zlib_ok = no], [
+  AC_MSG_ERROR([zlib not found])
   AC_SUBST(ZLIB_OBJS,[\${ZLIB_OBJS}])
   AC_SUBST(ZLIB_SRCS,[\${ZLIB_SRCS}])
   AC_SUBST(ZLIB_INCLUDE,[-I\${ZLIB_DIR}])
@@ -185,10 +186,11 @@ if test x"${libtommath_ok}" = x -o x"${libtommath_ok}" != xno; then
     libtommath_ok=no])])
 fi
 AS_IF([test $libtommath_ok = yes], [
-  AC_SUBST(TCL_PC_REQUIRES_PRIVATE, ['libtommath >= 1.2.0,'])
+  AC_SUBST(TCL_PC_REQUIRES_PRIVATE, ['']) # -ltommath in Libs
   AC_SUBST(TCL_PC_CFLAGS, ['-DTCL_WITH_EXTERNAL_TOMMATH'])
   AC_DEFINE(TCL_WITH_EXTERNAL_TOMMATH, 1, [Tcl with external libtommath])
 ], [
+  AC_MSG_ERROR([libtommath not found])
   AC_SUBST(TOMMATH_OBJS,[\${TOMMATH_OBJS}])
   AC_SUBST(TOMMATH_SRCS,[\${TOMMATH_SRCS}])
   AC_SUBST(TOMMATH_INCLUDE,[-I\${TOMMATH_DIR}])
@@ -964,6 +966,10 @@ AC_SUBST(EXTRA_TCLSH_LIBS)
 AC_SUBST(DLTEST_LD)
 AC_SUBST(DLTEST_SUFFIX)
 
+# For delayed configuration of extensions
+AC_SUBST(PKG_CONFIG)
+AC_SUBST(PKG_CONFIG_PATH)
+
 dnl	Disable the automake-friendly normalization of LIBOBJS
 dnl	performed by autoconf 2.53 and later.  It's not correct for us.
 define([_AC_LIBOBJS_NORMALIZE],[])