--- a/unix/configure
+++ b/unix/configure
@@ -18549,7 +18549,7 @@
 
 eval "TCL_LIB_FILE=${TCL_LIB_FILE}"
 
-TCL_LIBRARY='$(prefix)/lib/tcl$(VERSION)'
+test -z "$TCL_LIBRARY" && TCL_LIBRARY='$(prefix)/lib/tcl$(VERSION)'
 PRIVATE_INCLUDE_DIR='$(includedir)'
 HTML_DIR='$(DISTDIR)/html'
 
--- a/unix/configure.in
+++ b/unix/configure.in
@@ -773,7 +773,7 @@
 
 eval "TCL_LIB_FILE=${TCL_LIB_FILE}"
 
-TCL_LIBRARY='$(prefix)/lib/tcl$(VERSION)'
+test -z "$TCL_LIBRARY" && TCL_LIBRARY='$(prefix)/lib/tcl$(VERSION)'
 PRIVATE_INCLUDE_DIR='$(includedir)'
 HTML_DIR='$(DISTDIR)/html'