diff --git a/build/targets.blackbox.mak b/build/targets.blackbox.mak
index 0ca9e8a7e..1ba0af179 100644
--- a/build/targets.blackbox.mak
+++ b/build/targets.blackbox.mak
@@ -7,7 +7,7 @@ ion/src/blackbox/library_%.o: ion/src/blackbox/library.cpp
 	@echo "CXX     $@"
 	$(Q) $(CXX) $(SFLAGS) $(CXXFLAGS) -c $< -o $@
 
-libepsilon_objs = $(filter-out $(add-prefix ion/src/blackbox/,boot.o events.o),$(objs))
+libepsilon_objs = $(filter-out $(addprefix ion/src/blackbox/,boot.o events.o),$(objs))
 
 libepsilon_%.o: LDFLAGS += -exported_symbols_list ion/src/blackbox/lib_export_list.txt
 libepsilon_%.o: $(libepsilon_objs) $(app_objs) $(app_image_objs) ion/src/blackbox/library_%.o
diff --git a/ion/src/blackbox/compare.cpp b/ion/src/blackbox/compare.cpp
index eb82ea217..308ac946b 100644
--- a/ion/src/blackbox/compare.cpp
+++ b/ion/src/blackbox/compare.cpp
@@ -1,8 +1,11 @@
-// Compare_main
-
-// make -j8 PLATFORM=blackbox libepsilon_first.dylib
-// make -j8 PLATFORM=blackbox libepsilon_second.dylib
-//
+/* Compare two Epsilon versions
+ *
+ * git checkout first_hash
+ * make -j8 PLATFORM=blackbox clean libepsilon_first.dylib
+ * git checkout second_hash
+ * make -j8 PLATFORM=blackbox clean libepsilon_second.dylib
+ * make PLATFORM=blackbox compare
+ */
 
 #undef EPSILON_LIB_PREFIX
 #define EPSILON_LIB_PREFIX first
@@ -15,12 +18,12 @@
 #include <thread>
 
 int main(int argc, char * argv[]) {
-
   std::thread first(first_epsilon_main);
   std::thread second(second_epsilon_main);
 
   const KDColor * firstFrameBuffer = first_epsilon_frame_buffer();
   const KDColor * secondFrameBuffer = second_epsilon_frame_buffer();
+
   int index = 0;
   while (true) {
     int e = getchar();
@@ -41,8 +44,6 @@ int main(int argc, char * argv[]) {
       first_epsilon_write_frame_buffer_to_file("epsilon_first.png");
       second_epsilon_write_frame_buffer_to_file("epsilon_second.png");
       exit(-1);
-    } else {
-      //printf("Framebuffer at %p and %p were the same\n", firstFrameBuffer, secondFrameBuffer);
     }
   }