diff --git a/ssh.h b/ssh.h
index 2d285d23..1026a90b 100644
--- a/ssh.h
+++ b/ssh.h
@@ -322,9 +322,10 @@ unsigned long crc32_compute(const void *s, size_t len);
 unsigned long crc32_update(unsigned long crc_input, const void *s, size_t len);
 
 /* SSH CRC compensation attack detector */
-void *crcda_make_context(void);
-void crcda_free_context(void *handle);
-int detect_attack(void *handle, unsigned char *buf, uint32 len,
+struct crcda_ctx;
+struct crcda_ctx *crcda_make_context(void);
+void crcda_free_context(struct crcda_ctx *ctx);
+int detect_attack(struct crcda_ctx *ctx, unsigned char *buf, uint32 len,
 		  unsigned char *IV);
 
 /*
diff --git a/ssh1bpp.c b/ssh1bpp.c
index 7f5b72f6..5ace35fd 100644
--- a/ssh1bpp.c
+++ b/ssh1bpp.c
@@ -20,7 +20,7 @@ struct ssh1_bpp_state {
     const struct ssh_cipher *cipher;
     void *cipher_ctx;
 
-    void *crcda_ctx;
+    struct crcda_ctx *crcda_ctx;
 
     void *compctx, *decompctx;
 
diff --git a/sshcrcda.c b/sshcrcda.c
index 8d77cbb6..fe6598d3 100644
--- a/sshcrcda.c
+++ b/sshcrcda.c
@@ -55,7 +55,7 @@ struct crcda_ctx {
     uint32 n;
 };
 
-void *crcda_make_context(void)
+struct crcda_ctx *crcda_make_context(void)
 {
     struct crcda_ctx *ret = snew(struct crcda_ctx);
     ret->h = NULL;
@@ -63,9 +63,8 @@ void *crcda_make_context(void)
     return ret;
 }
 
-void crcda_free_context(void *handle)
+void crcda_free_context(struct crcda_ctx *ctx)
 {
-    struct crcda_ctx *ctx = (struct crcda_ctx *)handle;
     if (ctx) {
 	sfree(ctx->h);
 	ctx->h = NULL;
@@ -102,9 +101,8 @@ static int check_crc(uchar *S, uchar *buf, uint32 len, uchar *IV)
 }
 
 /* Detect a crc32 compensation attack on a packet */
-int detect_attack(void *handle, uchar *buf, uint32 len, uchar *IV)
+int detect_attack(struct crcda_ctx *ctx, uchar *buf, uint32 len, uchar *IV)
 {
-    struct crcda_ctx *ctx = (struct crcda_ctx *)handle;
     register uint32 i, j;
     uint32 l;
     register uchar *c;