diff --git a/xcconfig/NetNewsWire_project.xcconfig b/xcconfig/NetNewsWire_project.xcconfig
index 6f42ed57a..025e6300e 100644
--- a/xcconfig/NetNewsWire_project.xcconfig
+++ b/xcconfig/NetNewsWire_project.xcconfig
@@ -43,6 +43,9 @@ MACOSX_DEPLOYMENT_TARGET = 14.0
 IPHONEOS_DEPLOYMENT_TARGET = 17.0
 //SDKROOT = macosx
 SWIFT_SWIFT3_OBJC_INFERENCE = Off
+WARNING_CFLAGS = -Werror
+GCC_TREAT_WARNINGS_AS_ERRORS = YES
+SWIFT_TREAT_WARNINGS_AS_ERRORS = YES
 SWIFT_VERSION = 5.9
 
 // https://forums.swift.org/t/swift-packages-in-multiple-targets-results-in-this-will-result-in-duplication-of-library-code-errors/34892/33