diff --git a/b2sum/README.md b/b2sum/README.md
new file mode 100644
index 0000000..1fdaa17
--- /dev/null
+++ b/b2sum/README.md
@@ -0,0 +1,12 @@
+# b2sum #
+
+This is a simple tool to create BLAKE2 hashes of files or streams. For more usage information refer to the manpage, e.g., `man b2sum.1`.
+
+## Building and Installing ##
+
+To build `b2sum`, just run `make`. To install, run `make install`. The install path can be altered using the `PREFIX` variable, which defaults to `/usr/local`. Use `PREFIX=/some/path make install` to install somewhere else.
+
+`b2sum` makes use of OpenMP by default. Some compilers do not support this technology, in which case `b2sum` can be built without it using the `NO_OPENMP` variable. Use `NO_OPENMP=1 make` to build without OpenMP.
+
+For OS X, there is a prebuilt [Homebrew formula](https://github.com/Homebrew/homebrew-core/commit/e016cda47dfa298c6628de3e9d0fd976eecd91be) which may be installed with `brew install b2sum`.
+
diff --git a/b2sum/makefile b/b2sum/makefile
index 164cb26..4d19474 100644
--- a/b2sum/makefile
+++ b/b2sum/makefile
@@ -1,9 +1,13 @@
 PROG=b2sum
 PREFIX?=/usr/local
 MANDIR?=$(PREFIX)/man
+NO_OPENMP?=0
+NO_OPENMP_0=-fopenmp
+NO_OPENMP_1=
 CC?=gcc
-CFLAGS?=-O3 -march=native -static
-CFLAGS+=-I../sse -fopenmp
+CFLAGS?=-O3 -march=native -Werror=declaration-after-statement
+CFLAGS+=-std=c99 -I../sse
+CFLAGS+=$(NO_OPENMP_$(NO_OPENMP))
 LIBS=
 #FILES=b2sum.c ../ref/blake2b-ref.c ../ref/blake2s-ref.c ../ref/blake2bp-ref.c ../ref/blake2sp-ref.c 
 FILES=b2sum.c ../sse/blake2b.c ../sse/blake2s.c ../sse/blake2bp.c ../sse/blake2sp.c