diff --git a/packages/rtl-extra/src/aix/osdefs.inc b/packages/rtl-extra/src/aix/osdefs.inc
index a981f7d408..35bbc51800 100644
--- a/packages/rtl-extra/src/aix/osdefs.inc
+++ b/packages/rtl-extra/src/aix/osdefs.inc
@@ -22,3 +22,4 @@
 {define usedomain}             // Allow uname with "domain" entry.
                                 // (which is a GNU extension)
 
+{$define FPC_USE_LIBC}
\ No newline at end of file
diff --git a/packages/rtl-extra/src/bsd/osdefs.inc b/packages/rtl-extra/src/bsd/osdefs.inc
index 5f82f9cb0b..006f83e4b7 100644
--- a/packages/rtl-extra/src/bsd/osdefs.inc
+++ b/packages/rtl-extra/src/bsd/osdefs.inc
@@ -24,3 +24,7 @@
                                 // (which is a GNU extension)
 {$define hassysctl}             // Use sysctl unit
 
+{$ifdef darwin}
+  {$define FPC_USE_LIBC}
+{$endif}
+
diff --git a/packages/rtl-extra/src/solaris/osdefs.inc b/packages/rtl-extra/src/solaris/osdefs.inc
index a411f44a96..0ba5d31324 100644
--- a/packages/rtl-extra/src/solaris/osdefs.inc
+++ b/packages/rtl-extra/src/solaris/osdefs.inc
@@ -23,3 +23,4 @@
 {$define usedomain}             // Allow uname with "domain" entry.
                                 // (which is a GNU extension)
 
+{$define FPC_USE_LIBC}
\ No newline at end of file