diff --git a/Package.swift b/Package.swift
index a296279c7e..36937d039a 100644
--- a/Package.swift
+++ b/Package.swift
@@ -6,15 +6,10 @@ import PackageDescription
 
 var swiftSettings: [SwiftSetting] = [
     .define("SQLITE_ENABLE_FTS5"),
-    .enableUpcomingFeature("InferSendableFromCaptures"),
-    .enableUpcomingFeature("GlobalActorIsolatedTypesUsability"),
 ]
 var cSettings: [CSetting] = []
 var dependencies: [PackageDescription.Package.Dependency] = []
 
-// For Swift 5.8+
-//swiftSettings.append(.enableUpcomingFeature("ExistentialAny"))
-
 // Don't rely on those environment variables. They are ONLY testing conveniences:
 // $ SQLITE_ENABLE_PREUPDATE_HOOK=1 make test_SPM
 if ProcessInfo.processInfo.environment["SQLITE_ENABLE_PREUPDATE_HOOK"] == "1" {
@@ -81,7 +76,12 @@ let package = Package(
                 .copy("GRDBTests/Issue1383.sqlite"),
             ],
             cSettings: cSettings,
-            swiftSettings: swiftSettings)
+            swiftSettings: swiftSettings + [
+                // Tests still use the Swift 5 language mode.
+                .swiftLanguageMode(.v5),
+                .enableUpcomingFeature("InferSendableFromCaptures"),
+                .enableUpcomingFeature("GlobalActorIsolatedTypesUsability"),
+            ])
     ],
-    swiftLanguageModes: [.v5]
+    swiftLanguageModes: [.v6]
 )
diff --git a/SQLiteCustom/GRDB.xcconfig b/SQLiteCustom/GRDB.xcconfig
index bb0c769992..85a9b53165 100755
--- a/SQLiteCustom/GRDB.xcconfig
+++ b/SQLiteCustom/GRDB.xcconfig
@@ -13,3 +13,4 @@ OTHER_CFLAGS = -DUSING_BUILTIN_SQLITE -DGRDBCUSTOMSQLITE $(CUSTOM_SQLLIBRARY_CFL
 GCC_PREPROCESSOR_DEFINITIONS = "GRDBCUSTOMSQLITE=1"
 OTHER_SWIFT_FLAGS = -D USING_BUILTIN_SQLITE -D GRDBCUSTOMSQLITE $(CUSTOM_OTHER_SWIFT_FLAGS)
 HEADER_SEARCH_PATHS = $(SRCROOT)/SQLiteCustom/src
+SWIFT_VERSION = 6.0
diff --git a/SQLiteCustom/GRDBCustomSQLite-Testing.xcconfig b/SQLiteCustom/GRDBCustomSQLite-Testing.xcconfig
index 62178e5d3c..41762aa8c8 100755
--- a/SQLiteCustom/GRDBCustomSQLite-Testing.xcconfig
+++ b/SQLiteCustom/GRDBCustomSQLite-Testing.xcconfig
@@ -10,3 +10,7 @@ CUSTOM_OTHER_SWIFT_FLAGS=   // do not modify
 
 OTHER_CFLAGS = -DUSING_BUILTIN_SQLITE -DGRDBCUSTOMSQLITE $(CUSTOM_SQLLIBRARY_CFLAGS)        // Do not modify.
 OTHER_SWIFT_FLAGS = -D USING_BUILTIN_SQLITE -D GRDBCUSTOMSQLITE $(CUSTOM_OTHER_SWIFT_FLAGS)  // Do not modify.
+
+// Tests still use the Swift 5 language mode.
+SWIFT_UPCOMING_FEATURE_INFER_SENDABLE_FROM_CAPTURES = YES
+OTHER_SWIFT_FLAGS = $(inherited) -enable-upcoming-feature GlobalActorIsolatedTypesUsability
diff --git a/SQLiteCustom/GRDBDeploymentTarget.xcconfig b/SQLiteCustom/GRDBDeploymentTarget.xcconfig
index b4c8e9ed72..045b596962 100644
--- a/SQLiteCustom/GRDBDeploymentTarget.xcconfig
+++ b/SQLiteCustom/GRDBDeploymentTarget.xcconfig
@@ -2,5 +2,3 @@ IPHONEOS_DEPLOYMENT_TARGET = 13.0
 MACOSX_DEPLOYMENT_TARGET = 10.15
 TVOS_DEPLOYMENT_TARGET = 13.0
 WATCHOS_DEPLOYMENT_TARGET = 7.0
-SWIFT_UPCOMING_FEATURE_INFER_SENDABLE_FROM_CAPTURES = YES
-OTHER_SWIFT_FLAGS = $(inherited) -enable-upcoming-feature GlobalActorIsolatedTypesUsability
diff --git a/Support/GRDB.xcconfig b/Support/GRDB.xcconfig
index 5303f7a071..a3fabb0887 100644
--- a/Support/GRDB.xcconfig
+++ b/Support/GRDB.xcconfig
@@ -3,6 +3,7 @@ INFOPLIST_FILE = Support/Info.plist
 PRODUCT_NAME = GRDB
 PRODUCT_BUNDLE_IDENTIFIER = com.github.groue.$(PRODUCT_NAME:rfc1034identifier)
 MODULEMAP_FILE = $(SRCROOT)/Support/module.modulemap
+SWIFT_VERSION = 6.0
 
 // Slow compilation hunt:
 // OTHER_SWIFT_FLAGS = $(inherited) -Xfrontend -warn-long-expression-type-checking=100 -Xfrontend -warn-long-function-bodies=100
diff --git a/Support/GRDBDeploymentTarget.xcconfig b/Support/GRDBDeploymentTarget.xcconfig
index 76035ab53d..eb0e48eac5 100644
--- a/Support/GRDBDeploymentTarget.xcconfig
+++ b/Support/GRDBDeploymentTarget.xcconfig
@@ -3,8 +3,6 @@ MACOSX_DEPLOYMENT_TARGET = 10.15
 TVOS_DEPLOYMENT_TARGET = 13.0
 WATCHOS_DEPLOYMENT_TARGET = 7.0
 OTHER_SWIFT_FLAGS = $(inherited) -D SQLITE_ENABLE_FTS5
-SWIFT_UPCOMING_FEATURE_INFER_SENDABLE_FROM_CAPTURES = YES
-OTHER_SWIFT_FLAGS = $(inherited) -enable-upcoming-feature GlobalActorIsolatedTypesUsability
 
 //// Compile with all opt-in APIs
 //GCC_PREPROCESSOR_DEFINITIONS = $(inherited) GRDB_SQLITE_ENABLE_PREUPDATE_HOOK=1
diff --git a/Support/GRDBTests.xcconfig b/Support/GRDBTests.xcconfig
index 6cbc57782d..94ad777847 100644
--- a/Support/GRDBTests.xcconfig
+++ b/Support/GRDBTests.xcconfig
@@ -1 +1,5 @@
 #include "GRDBDeploymentTarget.xcconfig"
+
+// Tests still use the Swift 5 language mode.
+SWIFT_UPCOMING_FEATURE_INFER_SENDABLE_FROM_CAPTURES = YES
+OTHER_SWIFT_FLAGS = $(inherited) -enable-upcoming-feature GlobalActorIsolatedTypesUsability