diff --git a/include/boost/config/stdlib/libstdcpp3.hpp b/include/boost/config/stdlib/libstdcpp3.hpp
index a6bf80c3..ab9797bb 100644
--- a/include/boost/config/stdlib/libstdcpp3.hpp
+++ b/include/boost/config/stdlib/libstdcpp3.hpp
@@ -62,7 +62,13 @@
 #  undef BOOST_HAS_LONG_LONG
 #endif
 
-#if !defined(CYGWIN) 
+// Apple doesn't seem to reliably defined a *unix* macro
+#if !defined(CYGWIN) && (  defined(__unix__)  \
+                        || defined(__unix)    \
+                        || defined(unix)      \
+                        || defined(__APPLE__) \
+                        || defined(__APPLE)   \
+                        || defined(APPLE)
 #  include <unistd.h>
 #endif
 
diff --git a/include/boost/config/stdlib/sgi.hpp b/include/boost/config/stdlib/sgi.hpp
index fbbf669a..a1a6e7a8 100644
--- a/include/boost/config/stdlib/sgi.hpp
+++ b/include/boost/config/stdlib/sgi.hpp
@@ -40,7 +40,13 @@
 #  define BOOST_NO_STRINGSTREAM
 #endif
 
-#if !defined(CYGWIN)
+// Apple doesn't seem to reliably defined a *unix* macro
+#if !defined(CYGWIN) && (  defined(__unix__)  \
+                        || defined(__unix)    \
+                        || defined(unix)      \
+                        || defined(__APPLE__) \
+                        || defined(__APPLE)   \
+                        || defined(APPLE)
 #  include <unistd.h>
 #endif
 
diff --git a/include/boost/config/stdlib/stlport.hpp b/include/boost/config/stdlib/stlport.hpp
index 53bc10b2..66aaaaaf 100644
--- a/include/boost/config/stdlib/stlport.hpp
+++ b/include/boost/config/stdlib/stlport.hpp
@@ -16,7 +16,13 @@
 #  endif
 #endif
 
-#if !defined(CYGWIN) 
+// Apple doesn't seem to reliably defined a *unix* macro
+#if !defined(CYGWIN) && (  defined(__unix__)  \
+                        || defined(__unix)    \
+                        || defined(unix)      \
+                        || defined(__APPLE__) \
+                        || defined(__APPLE)   \
+                        || defined(APPLE)
 #  include <unistd.h>
 #endif
 
diff --git a/include/boost/config/stdlib/vacpp.hpp b/include/boost/config/stdlib/vacpp.hpp
index a92537bb..b61efa98 100644
--- a/include/boost/config/stdlib/vacpp.hpp
+++ b/include/boost/config/stdlib/vacpp.hpp
@@ -12,7 +12,13 @@
 #define BOOST_HAS_MACRO_USE_FACET
 #define BOOST_NO_STD_MESSAGES
 
-#if !defined(CYGWIN)
+// Apple doesn't seem to reliably defined a *unix* macro
+#if !defined(CYGWIN) && (  defined(__unix__)  \
+                        || defined(__unix)    \
+                        || defined(unix)      \
+                        || defined(__APPLE__) \
+                        || defined(__APPLE)   \
+                        || defined(APPLE)
 #  include <unistd.h>
 #endif