diff --git a/library/poly1305.c b/library/poly1305.c
index c22a0a1..b274119 100644
--- a/library/poly1305.c
+++ b/library/poly1305.c
@@ -289,7 +289,7 @@
 
 void mbedtls_poly1305_free( mbedtls_poly1305_context *ctx )
 {
-    if( ctx != NULL )
+    if( ctx == NULL )
         return;
 
     mbedtls_platform_zeroize( ctx, sizeof( mbedtls_poly1305_context ) );