diff --git a/block-sha1/sha1.h b/block-sha1/sha1.h
index b864df623e3..4df67477526 100644
--- a/block-sha1/sha1.h
+++ b/block-sha1/sha1.h
@@ -16,7 +16,7 @@ void blk_SHA1_Init(blk_SHA_CTX *ctx);
 void blk_SHA1_Update(blk_SHA_CTX *ctx, const void *dataIn, unsigned long len);
 void blk_SHA1_Final(unsigned char hashout[20], blk_SHA_CTX *ctx);
 
-#define git_SHA_CTX	blk_SHA_CTX
-#define git_SHA1_Init	blk_SHA1_Init
-#define git_SHA1_Update	blk_SHA1_Update
-#define git_SHA1_Final	blk_SHA1_Final
+#define platform_SHA_CTX	blk_SHA_CTX
+#define platform_SHA1_Init	blk_SHA1_Init
+#define platform_SHA1_Update	blk_SHA1_Update
+#define platform_SHA1_Final	blk_SHA1_Final
diff --git a/cache.h b/cache.h
index 22b7b812907..0d89ad8a3a9 100644
--- a/cache.h
+++ b/cache.h
@@ -11,13 +11,25 @@
 #include "string-list.h"
 
 #include SHA1_HEADER
-#ifndef git_SHA_CTX
-#define git_SHA_CTX	SHA_CTX
-#define git_SHA1_Init	SHA1_Init
-#define git_SHA1_Update	SHA1_Update
-#define git_SHA1_Final	SHA1_Final
+#ifndef platform_SHA_CTX
+/*
+ * platform's underlying implementation of SHA-1; could be OpenSSL,
+ * blk_SHA, Apple CommonCrypto, etc...  Note that including
+ * SHA1_HEADER may have already defined platform_SHA_CTX for our
+ * own implementations like block-sha1 and ppc-sha1, so we list
+ * the default for OpenSSL compatible SHA-1 implementations here.
+ */
+#define platform_SHA_CTX	SHA_CTX
+#define platform_SHA1_Init	SHA1_Init
+#define platform_SHA1_Update	SHA1_Update
+#define platform_SHA1_Final    	SHA1_Final
 #endif
 
+#define git_SHA_CTX		platform_SHA_CTX
+#define git_SHA1_Init		platform_SHA1_Init
+#define git_SHA1_Update		platform_SHA1_Update
+#define git_SHA1_Final		platform_SHA1_Final
+
 #include <zlib.h>
 typedef struct git_zstream {
 	z_stream z;
diff --git a/ppc/sha1.h b/ppc/sha1.h
index c405f734c20..9b24b326159 100644
--- a/ppc/sha1.h
+++ b/ppc/sha1.h
@@ -19,7 +19,7 @@ int ppc_SHA1_Init(ppc_SHA_CTX *c);
 int ppc_SHA1_Update(ppc_SHA_CTX *c, const void *p, unsigned long n);
 int ppc_SHA1_Final(unsigned char *hash, ppc_SHA_CTX *c);
 
-#define git_SHA_CTX	ppc_SHA_CTX
-#define git_SHA1_Init	ppc_SHA1_Init
-#define git_SHA1_Update	ppc_SHA1_Update
-#define git_SHA1_Final	ppc_SHA1_Final
+#define platform_SHA_CTX	ppc_SHA_CTX
+#define platform_SHA1_Init	ppc_SHA1_Init
+#define platform_SHA1_Update	ppc_SHA1_Update
+#define platform_SHA1_Final	ppc_SHA1_Final