diff --git a/lib/Makefile.am b/lib/Makefile.am
index 31dfe1bf9e..2e096f4760 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -22,7 +22,7 @@ libfcgi_sources = \
     coproc.cpp \
     filesys.cpp \
     hostinfo.cpp \
-    md5.c \
+    md5.cpp \
     md5_file.cpp \
     mfile.cpp \
     miofile.cpp \
@@ -47,7 +47,7 @@ generic_sources = \
     gui_rpc_client_ops.cpp \
     gui_rpc_client_print.cpp \
     hostinfo.cpp \
-    md5.c \
+    md5.cpp \
     md5_file.cpp \
     mem_usage.cpp \
     mfile.cpp \
diff --git a/lib/Makefile.mingw b/lib/Makefile.mingw
index 6ddf11a51e..0ce05c64bd 100644
--- a/lib/Makefile.mingw
+++ b/lib/Makefile.mingw
@@ -205,10 +205,6 @@ wrapper.o: $(BOINC_SRC)/samples/wrapper/wrapper.cpp
 %.o: $(BOINC_SRC)/samples/wrapper/%.c
 	$(CC) -c $< -o $@ $(CPPFLAGS) $(CFLAGS)
 
-# C-mode file
-md5.o: $(BOINC_SRC)/lib/md5.c
-	$(CXX) -c $(BOINC_SRC)/lib/md5.c -o md5.o $(CPPFLAGS) $(CXXFLAGS)
-
 # for boinc_zip. Don't change the order!
 zip:
 	mkdir -p $@
diff --git a/lib/md5.c b/lib/md5.cpp
similarity index 100%
rename from lib/md5.c
rename to lib/md5.cpp