diff --git a/ext/puma_http11/mini_ssl.c b/ext/puma_http11/mini_ssl.c
index e11f1fb9..7e0fd5e2 100644
--- a/ext/puma_http11/mini_ssl.c
+++ b/ext/puma_http11/mini_ssl.c
@@ -134,9 +134,13 @@ VALUE engine_init_server(VALUE self, VALUE mini_ssl_ctx) {
   ID sym_key = rb_intern("key");
   VALUE key = rb_funcall(mini_ssl_ctx, sym_key, 0);
 
+  StringValue(key);
+
   ID sym_cert = rb_intern("cert");
   VALUE cert = rb_funcall(mini_ssl_ctx, sym_cert, 0);
 
+  StringValue(cert);
+
   ID sym_ca = rb_intern("ca");
   VALUE ca = rb_funcall(mini_ssl_ctx, sym_ca, 0);
 
@@ -150,6 +154,7 @@ VALUE engine_init_server(VALUE self, VALUE mini_ssl_ctx) {
   SSL_CTX_use_PrivateKey_file(ctx, RSTRING_PTR(key), SSL_FILETYPE_PEM);
 
   if (!NIL_P(ca)) {
+    StringValue(ca);
     SSL_CTX_load_verify_locations(ctx, RSTRING_PTR(ca), NULL);
   }
   
diff --git a/lib/puma/minissl.rb b/lib/puma/minissl.rb
index 03bee97f..01eb822d 100644
--- a/lib/puma/minissl.rb
+++ b/lib/puma/minissl.rb
@@ -118,6 +118,11 @@ module Puma
           raise ArgumentError, "No such keystore file '#{keystore}'" unless File.exist? keystore
           @keystore = keystore
         end
+
+        def check
+          raise "Keystore not configured" unless @keystore
+        end
+
       else
         # non-jruby Context properties
         attr_reader :key
@@ -138,6 +143,11 @@ module Puma
           raise ArgumentError, "No such ca file '#{ca}'" unless File.exist? ca
           @ca = ca
         end
+
+        def check
+          raise "Key not configured" unless @key
+          raise "Cert not configured" unless @cert
+        end
       end
     end
 
@@ -156,6 +166,7 @@ module Puma
       end
 
       def accept
+        @ctx.check
         io = @socket.accept
         engine = Engine.server @ctx
 
@@ -163,6 +174,7 @@ module Puma
       end
 
       def accept_nonblock
+        @ctx.check
         io = @socket.accept_nonblock
         engine = Engine.server @ctx