diff --git a/configure.ac b/configure.ac
index cb31a242..51b1744d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -59,10 +59,10 @@ AX_CHECK_COMPILE_FLAG([-fcatch-undefined-c99-behavior],
 AX_CHECK_COMPILE_FLAG([-fno-strict-aliasing], [CFLAGS="$CFLAGS -fno-strict-aliasing"])
 AX_CHECK_COMPILE_FLAG([-fno-strict-overflow], [CFLAGS="$CFLAGS -fno-strict-overflow"])
 
-LIBTOOL_EXTRA_FLAGS=-version-info $SODIUM_LIBRARY_VERSION
+LIBTOOL_EXTRA_FLAGS="-version-info $SODIUM_LIBRARY_VERSION"
 case $host_os in
   cygwin* | mingw* | pw32* | cegcc*)
-    LIBTOOL_EXTRA_FLAGS=-module -avoid-version
+    LIBTOOL_EXTRA_FLAGS="-module -avoid-version"
     AX_CHECK_LINK_FLAG([-Wl,--dynamicbase], [LDFLAGS="$LDFLAGS -Wl,--dynamicbase"])
     AX_CHECK_LINK_FLAG([-Wl,--nxcompat], [LDFLAGS="$LDFLAGS -Wl,--nxcompat"])
     AX_CHECK_COMPILE_FLAG([-fstack-protector-all], [