diff --git a/hash.rs b/hash.rs
index 61f9c80f..3ace9751 100644
--- a/hash.rs
+++ b/hash.rs
@@ -99,7 +99,7 @@ impl Hasher {
 }
 
 impl Drop for Hasher {
-    fn drop(&self) {
+    fn drop(&mut self) {
         #[fixed_stack_segment]; #[inline(never)];
         unsafe {
             libcrypto::EVP_MD_CTX_destroy(self.ctx);
diff --git a/pkey.rs b/pkey.rs
index c6aac6d4..ce8bed91 100644
--- a/pkey.rs
+++ b/pkey.rs
@@ -361,7 +361,7 @@ impl PKey {
 }
 
 impl Drop for PKey {
-    fn drop(&self) {
+    fn drop(&mut self) {
         #[fixed_stack_segment]; #[inline(never)];
         unsafe {
             libcrypto::EVP_PKEY_free(self.evp);
diff --git a/symm.rs b/symm.rs
index b9353fcc..5f91909f 100644
--- a/symm.rs
+++ b/symm.rs
@@ -184,7 +184,7 @@ impl Crypter {
 }
 
 impl Drop for Crypter {
-    fn drop(&self) {
+    fn drop(&mut self) {
         #[fixed_stack_segment]; #[inline(never)];
         unsafe {
             libcrypto::EVP_CIPHER_CTX_free(self.ctx);