diff --git a/programs/pkey/pk_decrypt.c b/programs/pkey/pk_decrypt.c
index 1d8c959..1876ef3 100644
--- a/programs/pkey/pk_decrypt.c
+++ b/programs/pkey/pk_decrypt.c
@@ -62,7 +62,8 @@
 int main( int argc, char *argv[] )
 {
     FILE *f;
-    int ret = 1, c;
+    int ret = 1;
+    unsigned c;
     int exit_code = MBEDTLS_EXIT_FAILURE;
     size_t i, olen = 0;
     mbedtls_pk_context pk;