diff --git a/php/Makefile.am b/php/Makefile.am
index 5b50c0f..fad05c0 100644
--- a/php/Makefile.am
+++ b/php/Makefile.am
@@ -56,7 +56,7 @@ geos_la_CPPFLAGS = $(AM_CPPFLAGS) \
 	-I$(top_srcdir)/include
 
 install: all
-	$(INSTALL) -d "$(DESTDIR)"/`$(PHP_CONFIG) --extension-dir`
-	$(INSTALL) -m 755 .libs/geos.so "$(DESTDIR)"/`php-config --extension-dir`
+	$(INSTALL) -d "$(DESTDIR)"`$(PHP_CONFIG) --extension-dir`
+	$(INSTALL) -m 755 .libs/geos.so "$(DESTDIR)"`$(PHP_CONFIG) --extension-dir`
 
 endif
diff --git a/php/Makefile.in b/php/Makefile.in
index d8c343e..9485d0d 100644
--- a/php/Makefile.in
+++ b/php/Makefile.in
@@ -877,8 +877,8 @@ uninstall-am: uninstall-pkglibLTLIBRARIES
 
 
 @ENABLE_PHP_TRUE@install: all
-@ENABLE_PHP_TRUE@	$(INSTALL) -d "$(DESTDIR)"/`$(PHP_CONFIG) --extension-dir`
-@ENABLE_PHP_TRUE@	$(INSTALL) -m 755 .libs/geos.so "$(DESTDIR)"/`php-config --extension-dir`
+@ENABLE_PHP_TRUE@	$(INSTALL) -d "$(DESTDIR)"`$(PHP_CONFIG) --extension-dir`
+@ENABLE_PHP_TRUE@	$(INSTALL) -m 755 .libs/geos.so "$(DESTDIR)"`$(PHP_CONFIG) --extension-dir`
 
 # Tell versions [3.59,3.63) of GNU make to not export all variables.
 # Otherwise a system limit (for SysV at least) may be exceeded.