diff --git a/Makefile b/Makefile
index 1923562468..251368b315 100644
--- a/Makefile
+++ b/Makefile
@@ -492,20 +492,20 @@ include shared.mak
 # Define DC_SHA1 to enable the collision-detecting sha1
 # algorithm. This is slower, but may detect attempted collision attacks.
 #
-# Define BLK_SHA1 environment variable to make use of the bundled
-# optimized C SHA1 routine.
+# Define BLK_SHA1 to make use of optimized C SHA-1 routines bundled
+# with git (in the block-sha1/ directory).
 #
-# Define OPENSSL_SHA1 environment variable when running make to link
-# with the SHA1 routine from openssl library.
+# Define OPENSSL_SHA1 to link to the SHA-1 routines from the OpenSSL
+# library.
 #
 # ==== Options for the sha1collisiondetection library ====
 #
-# Define DC_SHA1_EXTERNAL in addition to DC_SHA1 if you want to build / link
+# Define DC_SHA1_EXTERNAL if you want to build / link
 # git with the external SHA1 collision-detect library.
 # Without this option, i.e. the default behavior is to build git with its
 # own built-in code (or submodule).
 #
-# Define DC_SHA1_SUBMODULE in addition to DC_SHA1 to use the
+# Define DC_SHA1_SUBMODULE to use the
 # sha1collisiondetection shipped as a submodule instead of the
 # non-submodule copy in sha1dc/. This is an experimental option used
 # by the git project to migrate to using sha1collisiondetection as a