diff --git a/configure.ac b/configure.ac
index 63c78c38..1aa460ec 100644
--- a/configure.ac
+++ b/configure.ac
@@ -208,14 +208,18 @@ AC_FLDIGI_OSS
 # Set ac_cv_png to yes/no    (not used)
 # Define USE_PNG in config.h (as above)
 # Substitute PNG_CFLAGS and PNG_LIBS in Makefile
-AC_FLDIGI_PKG_CHECK([png], [libpng >= 1.2.8], [$ac_cv_want_fldigi], [no])
+if test "x$ac_cv_want_fldigi" = "xyes"; then
+    AC_FLDIGI_PKG_CHECK([png], [libpng >= 1.2.8], [no], [no])
+fi
 
 ### libsamplerate
 # Required if $ac_cv_want_fldigi is "yes"
 # Set ac_cv_samplerate to yes/no    (not used)
 # Define USE_SAMPLERATE in config.h (as above)
 # Substitute SAMPLERATE_CFLAGS and SAMPLERATE_LIBS in Makefile
-AC_FLDIGI_PKG_CHECK([samplerate], [samplerate >= 0.1.1], [$ac_cv_want_fldigi], [no])
+if test "x$ac_cv_want_fldigi" = "xyes"; then
+    AC_FLDIGI_PKG_CHECK([samplerate], [samplerate >= 0.1.1], [no], [no])
+fi
 
 ### libsndfile
 # Set ac_cv_sndfile to yes/no