diff --git a/libpeas/peas-extension-set.c b/libpeas/peas-extension-set.c
index e306316..d21e8b5 100644
--- a/libpeas/peas-extension-set.c
+++ b/libpeas/peas-extension-set.c
@@ -497,12 +497,18 @@ peas_extension_set_call_valist (PeasExtensionSet *set,
 {
   GICallableInfo *callable_info;
   GIArgument *args;
+  gint n_args;
 
   g_return_val_if_fail (PEAS_IS_EXTENSION_SET (set), FALSE);
   g_return_val_if_fail (method_name != NULL, FALSE);
 
   callable_info = peas_gi_get_method_info (set->priv->exten_type, method_name);
-  args = g_newa (GIArgument, g_callable_info_get_n_args (callable_info));
+  g_return_val_if_fail (callable_info != NULL, FALSE);
+
+  n_args = g_callable_info_get_n_args (callable_info);
+  g_return_val_if_fail (n_args >= 0, FALSE);
+
+  args = g_newa (GIArgument, n_args);
   peas_gi_valist_to_arguments (callable_info, va_args, args, NULL);
 
   return peas_extension_set_callv (set, method_name, args);
diff --git a/libpeas/peas-extension-subclasses.c b/libpeas/peas-extension-subclasses.c
index 9231eca..0f48c11 100644
--- a/libpeas/peas-extension-subclasses.c
+++ b/libpeas/peas-extension-subclasses.c
@@ -59,7 +59,7 @@ handle_method_impl (ffi_cif  *cif,
   GIArgInfo *arg_info;
   GITypeInfo *type_info;
   GITypeInfo *return_type_info;
-  guint n_args, i;
+  gint n_args, i;
   PeasExtension *instance;
   GIArgument *arguments;
   GIArgument return_value;
@@ -68,6 +68,7 @@ handle_method_impl (ffi_cif  *cif,
   g_assert (PEAS_IS_EXTENSION (instance));
 
   n_args = g_callable_info_get_n_args (impl->info);
+  g_return_if_fail (n_args < 1);
   arguments = g_newa (GIArgument, n_args-1);
 
   for (i = 1; i < n_args; i++)
@@ -191,6 +192,7 @@ implement_interface_methods (gpointer iface,
            g_type_name (exten_type), g_type_name (proxy_type));
 
   iface_info = g_irepository_find_by_gtype (NULL, exten_type);
+  g_return_if_fail (iface_info != NULL);
   g_return_if_fail (g_base_info_get_type (iface_info) == GI_INFO_TYPE_INTERFACE);
 
   n_vfuncs = g_interface_info_get_n_vfuncs (iface_info);
diff --git a/libpeas/peas-extension.c b/libpeas/peas-extension.c
index 83f0e5f..63accb1 100644
--- a/libpeas/peas-extension.c
+++ b/libpeas/peas-extension.c
@@ -217,6 +217,7 @@ peas_extension_call_valist (PeasExtension *exten,
   GIArgument retval;
   gpointer retval_ptr;
   gboolean ret;
+  gint n_args;
 
   g_return_val_if_fail (PEAS_IS_EXTENSION (exten), FALSE);
   g_return_val_if_fail (method_name != NULL, FALSE);
@@ -225,7 +226,9 @@ peas_extension_call_valist (PeasExtension *exten,
   if (callable_info == NULL)
     return FALSE;
 
-  gargs = g_newa (GIArgument, g_callable_info_get_n_args (callable_info));
+  n_args = g_callable_info_get_n_args (callable_info);
+  g_return_val_if_fail (n_args >= 0, FALSE);
+  gargs = g_newa (GIArgument, n_args);
   peas_gi_valist_to_arguments (callable_info, args, gargs, &retval_ptr);
 
   ret = peas_extension_callv (exten, method_name, gargs, &retval);
diff --git a/libpeas/peas-introspection.c b/libpeas/peas-introspection.c
index e93ec51..3431721 100644
--- a/libpeas/peas-introspection.c
+++ b/libpeas/peas-introspection.c
@@ -31,12 +31,14 @@ peas_gi_valist_to_arguments (GICallableInfo *callable_info,
                              GIArgument     *arguments,
                              gpointer       *return_value)
 {
-  guint i, n_args;
+  gint i, n_args;
   GIArgInfo *arg_info;
   GITypeInfo *arg_type_info;
   GITypeInfo *retval_info;
   GIArgument *cur_arg;
 
+  g_return_if_fail (callable_info);
+
   n_args = g_callable_info_get_n_args (callable_info);
 
   for (i = 0; i < n_args; i++)
@@ -144,9 +146,11 @@ peas_gi_split_in_and_out_arguments (GICallableInfo *callable_info,
                                     GIArgument     *out_args,
                                     guint          *n_out_args)
 {
-  guint n_args, i;
+  gint n_args, i;
   GIArgInfo *arg_info;
 
+  g_return_if_fail (callable_info != NULL);
+
   n_args = g_callable_info_get_n_args (callable_info);
 
   for (i = 0; i < n_args; i++)
@@ -347,7 +351,8 @@ peas_method_apply (GObject     *instance,
                    GIArgument  *return_value)
 {
   GICallableInfo *func_info;
-  guint n_args, n_in_args, n_out_args;
+  gint n_args;
+  guint n_in_args, n_out_args;
   GIArgument *in_args, *out_args;
   gboolean ret = TRUE;
   GError *error = NULL;
@@ -357,6 +362,7 @@ peas_method_apply (GObject     *instance,
     return FALSE;
 
   n_args = g_callable_info_get_n_args (func_info);
+  g_return_val_if_fail (n_args >= 0, FALSE);
   n_in_args = 0;
   n_out_args = 0;
 
diff --git a/loaders/seed/peas-extension-seed.c b/loaders/seed/peas-extension-seed.c
index e5327bb..ab8e999 100644
--- a/loaders/seed/peas-extension-seed.c
+++ b/loaders/seed/peas-extension-seed.c
@@ -235,7 +235,8 @@ peas_extension_seed_call (PeasExtension *exten,
   SeedValue js_method;
   GICallableInfo *func_info;
   GITypeInfo *retval_info;
-  guint n_args, n_in_args, n_out_args, i;
+  gint n_args;
+  guint n_in_args, n_out_args, i;
   SeedValue *js_in_args;
   OutArg *out_args;
   SeedValue js_ret, val;
@@ -268,7 +269,11 @@ peas_extension_seed_call (PeasExtension *exten,
 
   /* Prepare the arguments */
   func_info = peas_gi_get_method_info (exten_type, method_name);
+  if (func_info == NULL)
+    return FALSE;
+
   n_args = g_callable_info_get_n_args (func_info);
+  g_return_val_if_fail (n_args >= 0, FALSE);
   n_in_args = 0;
   n_out_args = 0;
 
