diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1917eb784b3..d0dd335680e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+### Improvements
+
+- Improve compiler error message for missing Swift declarations due to APPLICATION_EXTENSION_API_ONLY (#4603)
+
 ## 8.42.0-beta.2
 
 ### Fixes
diff --git a/Sentry.podspec b/Sentry.podspec
index 5de0712a748..d550d86a319 100644
--- a/Sentry.podspec
+++ b/Sentry.podspec
@@ -24,7 +24,8 @@ Pod::Spec.new do |s|
       # APPLICATION_EXTENSION_API_ONLY has a side effect of exposing all `@objc` marked entities in `Sentry-Swift.h` (regardless of access level)
       # This is currently needed for Sentry module to compile. Changing this to NO will break the build.
       'APPLICATION_EXTENSION_API_ONLY' => 'YES',
-      'SWIFT_INCLUDE_PATHS' => '${PODS_TARGET_SRCROOT}/Sources/Sentry/include'
+      'SWIFT_INCLUDE_PATHS' => '${PODS_TARGET_SRCROOT}/Sources/Sentry/include',
+      'OTHER_CFLAGS' => '$(inherited) -DAPPLICATION_EXTENSION_API_ONLY_$(APPLICATION_EXTENSION_API_ONLY)'
   }
   s.watchos.pod_target_xcconfig = {
       'OTHER_LDFLAGS' => '$(inherited) -framework WatchKit'
diff --git a/Sentry.xcodeproj/project.pbxproj b/Sentry.xcodeproj/project.pbxproj
index 60898b55ea9..fad17aaa0dd 100644
--- a/Sentry.xcodeproj/project.pbxproj
+++ b/Sentry.xcodeproj/project.pbxproj
@@ -5329,7 +5329,6 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = 63AA75C51EB8B00100D153DE /* Sentry.xcconfig */;
 			buildSettings = {
-				APPLICATION_EXTENSION_API_ONLY = YES;
 				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_WARN_ASSIGN_ENUM = NO;
@@ -5350,7 +5349,6 @@
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
 				LD_DYLIB_INSTALL_NAME = "$(DYLIB_INSTALL_NAME_BASE:standardizepath)/$(EXECUTABLE_PATH)";
 				MODULEMAP_PRIVATE_FILE = "";
-				OTHER_CFLAGS = "-DCARTHAGE_$(CARTHAGE)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_VERSION = 5.0;
@@ -5362,7 +5360,6 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = 63AA75C51EB8B00100D153DE /* Sentry.xcconfig */;
 			buildSettings = {
-				APPLICATION_EXTENSION_API_ONLY = YES;
 				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_WARN_ASSIGN_ENUM = NO;
@@ -5388,7 +5385,6 @@
 					"@loader_path/Frameworks",
 				);
 				MODULEMAP_PRIVATE_FILE = "";
-				OTHER_CFLAGS = "-DCARTHAGE_$(CARTHAGE)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
 				SWIFT_VERSION = 5.0;
 				USE_HEADERMAP = YES;
@@ -5520,7 +5516,6 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = 63AA75C51EB8B00100D153DE /* Sentry.xcconfig */;
 			buildSettings = {
-				APPLICATION_EXTENSION_API_ONLY = YES;
 				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_WARN_ASSIGN_ENUM = NO;
@@ -5546,7 +5541,6 @@
 					"@loader_path/Frameworks",
 				);
 				MODULEMAP_PRIVATE_FILE = "";
-				OTHER_CFLAGS = "-DCARTHAGE_$(CARTHAGE)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_VERSION = 5.0;
@@ -5646,7 +5640,6 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = 63AA75C51EB8B00100D153DE /* Sentry.xcconfig */;
 			buildSettings = {
-				APPLICATION_EXTENSION_API_ONLY = YES;
 				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_WARN_ASSIGN_ENUM = NO;
@@ -5672,7 +5665,6 @@
 					"@loader_path/Frameworks",
 				);
 				MODULEMAP_PRIVATE_FILE = "";
-				OTHER_CFLAGS = "-DCARTHAGE_$(CARTHAGE)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_VERSION = 5.0;
@@ -6123,7 +6115,6 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = 63AA75C51EB8B00100D153DE /* Sentry.xcconfig */;
 			buildSettings = {
-				APPLICATION_EXTENSION_API_ONLY = YES;
 				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_WARN_ASSIGN_ENUM = NO;
@@ -6149,7 +6140,6 @@
 					"@loader_path/Frameworks",
 				);
 				MODULEMAP_PRIVATE_FILE = "";
-				OTHER_CFLAGS = "-DCARTHAGE_$(CARTHAGE)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
 				SWIFT_VERSION = 5.0;
 				USE_HEADERMAP = YES;
@@ -6351,7 +6341,6 @@
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = 63AA75C51EB8B00100D153DE /* Sentry.xcconfig */;
 			buildSettings = {
-				APPLICATION_EXTENSION_API_ONLY = YES;
 				BUILD_LIBRARY_FOR_DISTRIBUTION = YES;
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_WARN_ASSIGN_ENUM = NO;
@@ -6377,7 +6366,6 @@
 					"@loader_path/Frameworks",
 				);
 				MODULEMAP_PRIVATE_FILE = "";
-				OTHER_CFLAGS = "-DCARTHAGE_$(CARTHAGE)";
 				PROVISIONING_PROFILE_SPECIFIER = "";
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_VERSION = 5.0;
diff --git a/Sources/Configuration/Sentry.xcconfig b/Sources/Configuration/Sentry.xcconfig
index 5bda006b0a1..f4e5181152f 100644
--- a/Sources/Configuration/Sentry.xcconfig
+++ b/Sources/Configuration/Sentry.xcconfig
@@ -21,3 +21,8 @@ PRODUCT_BUNDLE_IDENTIFIER = io.sentry.$(PRODUCT_MODULE_NAME)
 MODULEMAP_FILE = $(SRCROOT)/Sources/Resources/$(PRODUCT_MODULE_NAME_$(CONFIGURATION)).modulemap
 ARCHS = $(ARCHS_STANDARD) arm64e
 ARCHS[sdk=*simulator] = $(ARCHS_STANDARD)
+
+// APPLICATION_EXTENSION_API_ONLY YES causes a side effect of exposing all @objc classes to Sentry-Swift.h
+// and without it the project wont compile.
+APPLICATION_EXTENSION_API_ONLY = YES
+OTHER_CFLAGS = -DCARTHAGE_$(CARTHAGE) -DAPPLICATION_EXTENSION_API_ONLY_$(APPLICATION_EXTENSION_API_ONLY)
diff --git a/Sources/Sentry/Public/SentryDefines.h b/Sources/Sentry/Public/SentryDefines.h
index a6e9e6be2a8..3634ebc8aba 100644
--- a/Sources/Sentry/Public/SentryDefines.h
+++ b/Sources/Sentry/Public/SentryDefines.h
@@ -1,5 +1,26 @@
 #import <Foundation/Foundation.h>
 
+// SentryDefines.h is a key header and will be checked early,
+// ensuring this error appears first during the compile process.
+//
+// Setting APPLICATION_EXTENSION_API_ONLY to YES has a side effect of
+// including all Swift classes in the `Sentry-Swift.h` header which is
+// required for the SDK to work.
+//
+// https://github.com/getsentry/sentry-cocoa/issues/4426
+//
+// This mainly came up in RN SDK, because
+// some libraries advice to users
+// to set APPLICATION_EXTENSION_API_ONLY_NO
+// for all cocoapods targets, instead of
+// only to their pod.
+// https://github.com/getsentry/sentry-react-native/issues/3908
+#if APPLICATION_EXTENSION_API_ONLY_NO
+#    error "Set APPLICATION_EXTENSION_API_ONLY to YES in the Sentry build settings.\
+ Setting the flag to YES is required for the SDK to work.\
+ For more information, visit https://docs.sentry.io/platforms/apple/troubleshooting/#unknown-receiver-somereceiver-use-of-undeclared-identifier-someidentifier
+#endif
+
 #ifdef __cplusplus
 #    define SENTRY_EXTERN extern "C" __attribute__((visibility("default")))
 #else