diff --git a/mibuild/altera_quartus.py b/mibuild/altera_quartus.py
index 8783201da..cfda1cf06 100644
--- a/mibuild/altera_quartus.py
+++ b/mibuild/altera_quartus.py
@@ -77,6 +77,7 @@ quartus_sta {build_name}.qpf
 		raise OSError("Subprocess failed")
 
 class AlteraQuartusPlatform(GenericPlatform):
+	bitstream_ext = ".sof"
 	def build(self, fragment, build_dir="build", build_name="top",
 			quartus_path="/opt/Altera", run=True):
 		tools.mkdir_noerror(build_dir)
diff --git a/mibuild/xilinx_ise.py b/mibuild/xilinx_ise.py
index cc0893288..8bab531a0 100644
--- a/mibuild/xilinx_ise.py
+++ b/mibuild/xilinx_ise.py
@@ -184,6 +184,7 @@ class XilinxMultiReg:
 		return XilinxMultiRegImpl(dr.i, dr.o, dr.odomain, dr.n)
 
 class XilinxISEPlatform(GenericPlatform):
+	bitstream_ext = ".bit"
 	xst_opt = """-ifmt MIXED
 -opt_mode SPEED
 -reduce_control_sets auto