diff --git a/simgear/props/props_io.hxx b/simgear/props/props_io.hxx
index 34fe33a3..d13f4d1f 100644
--- a/simgear/props/props_io.hxx
+++ b/simgear/props/props_io.hxx
@@ -20,8 +20,7 @@
 #include STL_STRING
 #include <vector>
 #include <map>
-#include <istream>
-#include <ostream>
+#include <iosfwd>
 
 /**
  * Read properties from an XML input stream.
diff --git a/simgear/structure/SGSmplhist.hxx b/simgear/structure/SGSmplhist.hxx
index 7d9f05d3..36ddc502 100644
--- a/simgear/structure/SGSmplhist.hxx
+++ b/simgear/structure/SGSmplhist.hxx
@@ -25,8 +25,7 @@ Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 #endif
 #define SampleHistogram_h 1
 
-#include <ostream>
-#include <fstream>
+#include <iosfwd>
 #include "SGSmplstat.hxx"
 
 extern const int SampleHistogramMinimum;