diff --git a/.gitignore b/.gitignore
index bd417de..1fa0a25 100644
--- a/.gitignore
+++ b/.gitignore
@@ -35,3 +35,4 @@ assembler/test.map
 ### test program files
 *.ram
 *.map
+Vivado
diff --git a/assembler/Makefile b/assembler/Makefile
index 8d0778f..67676be 100644
--- a/assembler/Makefile
+++ b/assembler/Makefile
@@ -11,7 +11,7 @@ IDIR=inc
 ODIR=obj
 SDIR=src
 
-CFLAGS = -Wall
+CFLAGS = -fcommon -Wall
 
 _DEPS = command.h files.h labels.h
 DEPS = $(patsubst %,$(IDIR)/%,$(_DEPS))