diff --git a/Makefile.in b/Makefile.in
index ddf9060..e2367ba 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -1,6 +1,6 @@
 
 CC= @CC@
-CSTD= @CSTD@ -Wall -D_POSIX_C_SOURCE=200112L
+CSTD= @CSTD@ -Wall
 CFLAGS= $(CSTD) @CFLAGS@ -DED25519_@ED25519IMPL@ @MYDEFS@
 ASFLAGS=
 LDFLAGS= @NOPIE@
diff --git a/main.c b/main.c
index 3ba56b4..c01b20d 100644
--- a/main.c
+++ b/main.c
@@ -1,3 +1,7 @@
+#ifdef __linux__
+#define _POSIX_C_SOURCE 200112L
+#endif
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>