diff --git a/clib/sha1.h b/clib/sha1.h
--- a/clib/sha1.h
+++ b/clib/sha1.h
@@ -13,6 +13,7 @@
 extern "C" {
 #endif
 
+#ifdef SHA1_USE_SHA1DC
 #include <stdlib.h>
 #include <sha1dc/sha1.h>
 
@@ -34,6 +35,24 @@
 static inline int fbhg_sha1_final(unsigned char* md, fbhg_sha1_ctx_t* ctx) {
   return SHA1DCFinal(md, ctx);
 }
+#else
+#include <openssl/sha.h>
+
+typedef SHA_CTX fbhg_sha1_ctx_t;
+
+static inline int fbhg_sha1_init(fbhg_sha1_ctx_t* ctx) {
+  return SHA1_Init(ctx);
+}
+
+static inline int
+fbhg_sha1_update(fbhg_sha1_ctx_t* ctx, const void* data, unsigned long length) {
+  return SHA1_Update(ctx, data, length);
+}
+
+static inline int fbhg_sha1_final(unsigned char* md, fbhg_sha1_ctx_t* ctx) {
+  return SHA1_Final(md, ctx);
+}
+#endif
 
 #ifdef __cplusplus
 } /* extern C */
diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -16,6 +16,8 @@
 WEXTRA = "" if iswindows else "-Wextra"
 WCONVERSION = "" if iswindows else "-Wconversion"
 PEDANTIC = "" if iswindows else "-pedantic"
+SHA1LIB_DEFINE = "/DSHA1_USE_SHA1DC" if iswindows else "-DSHA1_USE_SHA1DC"
+SHA1_LIBRARY = "sha1detectcoll"
 NOOPTIMIZATION = "/Od" if iswindows else "-O0"
 OPTIMIZATION = "" if iswindows else "-O2"
 PRODUCEDEBUGSYMBOLS = "/DEBUG:FULL" if iswindows else "-g"
@@ -52,7 +54,7 @@
 
 sys.argv = args
 
-cflags = []
+cflags = [SHA1LIB_DEFINE]
 
 # if this is set, compile all C extensions with -O0 -g for easy debugging.  note
 # that this is not manifested in any way in the Makefile dependencies.
@@ -160,7 +162,7 @@
         'datapack': {
             "sources" : ["cdatapack/cdatapack.c"],
             "include_dirs" : ["clib"] + include_dirs,
-            "libraries" : ["lz4", "sha1detectcoll"],
+            "libraries" : ["lz4", SHA1_LIBRARY],
             "extra_args" : filter(None,
                 [STDC99, WALL, WERROR, WSTRICTPROTOTYPES] + cflags),
         },
@@ -259,7 +261,7 @@
                     'datapack',
                     'lz4',
                     'mpatch',
-                    'sha1detectcoll',
+                    SHA1_LIBRARY,
                 ],
                 extra_compile_args=filter(None, [STDCPP0X, WALL] + cflags),
             ),
@@ -287,7 +289,7 @@
                     'third-party',
                 ] + include_dirs,
                 library_dirs=library_dirs,
-                libraries=['sha1detectcoll'],
+                libraries=[SHA1_LIBRARY],
                 extra_compile_args=filter(None, [
                     STDC99,
                     WALL,