diff --git a/tools/cryptorf/Makefile b/tools/cryptorf/Makefile
index 293194f03..45cd51a5d 100644
--- a/tools/cryptorf/Makefile
+++ b/tools/cryptorf/Makefile
@@ -3,7 +3,14 @@ MYSRCS = cryptolib.c util.c
 MYINCLUDES = -I../../common/cryptorf
 MYCFLAGS =
 MYDEFS =
-MYLDLIBS = -lpthread -latomic
+
+# Atomic
+# RPi Zero gcc requires -latomic
+# but MacOSX /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld
+# doesn't recognize option --as-needed
+ifneq ($(platform),Darwin)
+    MYLDLIBS += -lpthread -Wl,--as-needed -latomic -Wl,--no-as-needed
+endif
 
 BINS = cm sm sma sma_multi
 INSTALLTOOLS = $(BINS)