diff --git a/winpr/libwinpr/crt/string.c b/winpr/libwinpr/crt/string.c
index 4015108f5..2717ac06d 100644
--- a/winpr/libwinpr/crt/string.c
+++ b/winpr/libwinpr/crt/string.c
@@ -98,6 +98,9 @@ size_t _wcslen(const WCHAR* str)
 {
 	WCHAR* p = (WCHAR*) str;
 
+	if (!p)
+		return 0;
+
 	while (*p)
 		p++;
 
diff --git a/winpr/libwinpr/sspi/NTLM/ntlm.c b/winpr/libwinpr/sspi/NTLM/ntlm.c
index 11258adf7..adc0d0d79 100644
--- a/winpr/libwinpr/sspi/NTLM/ntlm.c
+++ b/winpr/libwinpr/sspi/NTLM/ntlm.c
@@ -63,6 +63,11 @@ void ntlm_SetContextWorkstation(NTLM_CONTEXT* context, char* Workstation)
 void ntlm_SetContextServicePrincipalNameW(NTLM_CONTEXT* context, LPWSTR ServicePrincipalName)
 {
 	context->ServicePrincipalName.Length = _wcslen(ServicePrincipalName) * 2;
+	if (!ServicePrincipalName)
+	{
+		context->ServicePrincipalName.Buffer = NULL;
+		return;
+	}
 	context->ServicePrincipalName.Buffer = (PWSTR) malloc(context->ServicePrincipalName.Length + 2);
 	CopyMemory(context->ServicePrincipalName.Buffer, ServicePrincipalName, context->ServicePrincipalName.Length + 2);
 }