diff --git a/historic/jam/src/jam.h b/historic/jam/src/jam.h
index 18bfa4709..b6c45c72a 100644
--- a/historic/jam/src/jam.h
+++ b/historic/jam/src/jam.h
@@ -231,10 +231,14 @@
 # define OSMINOR "OS=CYGWIN"
 # define OS_CYGWIN
 # endif
-# ifdef __FreeBSD__
+# if defined(__FreeBSD__) && !defined(__DragonFly__)
 # define OSMINOR "OS=FREEBSD"
 # define OS_FREEBSD
 # endif
+# ifdef __DragonFly__
+# define OSMINOR "OS=DRAGONFLYBSD"
+# define OS_DRAGONFLYBSD
+# endif
 # ifdef __DGUX__
 # define OSMINOR "OS=DGUX"
 # define OS_DGUX
@@ -394,6 +398,7 @@
 
 # if !defined(OS_BSDI) && \
      !defined(OS_FREEBSD) && \
+     !defined(OS_DRAGONFLYBSD) && \
      !defined(OS_NEXT) && \
      !defined(OS_MACHTEN) && \
      !defined(OS_MACOSX) && \
@@ -426,6 +431,7 @@
      defined( __i386__ ) || \
      defined( _M_IX86 )
 # if !defined( OS_FREEBSD ) && \
+     !defined( OS_DRAGONFLYBSD ) && \
      !defined( OS_OS2 ) && \
      !defined( OS_AS400 )
 # define OSPLAT "OSPLAT=X86"
diff --git a/jam_src/jam.h b/jam_src/jam.h
index 18bfa4709..b6c45c72a 100644
--- a/jam_src/jam.h
+++ b/jam_src/jam.h
@@ -231,10 +231,14 @@
 # define OSMINOR "OS=CYGWIN"
 # define OS_CYGWIN
 # endif
-# ifdef __FreeBSD__
+# if defined(__FreeBSD__) && !defined(__DragonFly__)
 # define OSMINOR "OS=FREEBSD"
 # define OS_FREEBSD
 # endif
+# ifdef __DragonFly__
+# define OSMINOR "OS=DRAGONFLYBSD"
+# define OS_DRAGONFLYBSD
+# endif
 # ifdef __DGUX__
 # define OSMINOR "OS=DGUX"
 # define OS_DGUX
@@ -394,6 +398,7 @@
 
 # if !defined(OS_BSDI) && \
      !defined(OS_FREEBSD) && \
+     !defined(OS_DRAGONFLYBSD) && \
      !defined(OS_NEXT) && \
      !defined(OS_MACHTEN) && \
      !defined(OS_MACOSX) && \
@@ -426,6 +431,7 @@
      defined( __i386__ ) || \
      defined( _M_IX86 )
 # if !defined( OS_FREEBSD ) && \
+     !defined( OS_DRAGONFLYBSD ) && \
      !defined( OS_OS2 ) && \
      !defined( OS_AS400 )
 # define OSPLAT "OSPLAT=X86"
diff --git a/v1/gcc-tools.jam b/v1/gcc-tools.jam
index a0784bc61..f32f32b6d 100644
--- a/v1/gcc-tools.jam
+++ b/v1/gcc-tools.jam
@@ -129,6 +129,13 @@ else if $(UNIX)
         flags gcc LINKFLAGS <threading>multi : -pthread ;
         # there is no -lrt on BSD
         }
+    case DragonFly :
+        {
+        flags gcc CFLAGS <threading>multi : -pthread ;
+        flags gcc LINKFLAGS <threading>multi : -pthread ;
+        # there is no -lrt on BSD - DragonFly is a FreeBSD variant,
+        # which anoyingly doesn't say it's a *BSD.
+        }
     case IRIX :
         {
         # gcc on IRIX does not support multi-threading, don't set anything here.
diff --git a/v2/tools/gcc.jam b/v2/tools/gcc.jam
index 6800862d2..48d9b9e8c 100644
--- a/v2/tools/gcc.jam
+++ b/v2/tools/gcc.jam
@@ -298,6 +298,12 @@ else if [ modules.peek : UNIX ]
         flags gcc OPTIONS <threading>multi : -pthread ;
         # there is no -lrt on BSD
         }
+    case DragonFly :
+        {
+        flags gcc OPTIONS <threading>multi : -pthread ;
+        # there is no -lrt on BSD - DragonFly is a FreeBSD variant,
+        # which anoyingly doesn't say it's a *BSD.
+        }
     case IRIX :
         {
         # gcc on IRIX does not support multi-threading, don't set anything here.