diff --git a/Sources/SWBCore/Dependencies.swift b/Sources/SWBCore/Dependencies.swift
index de31a838..2dd8946a 100644
--- a/Sources/SWBCore/Dependencies.swift
+++ b/Sources/SWBCore/Dependencies.swift
@@ -302,17 +302,18 @@ public struct HeaderDependenciesContext: Sendable, SerializableCodable {
             data: DiagnosticData("The current toolchain does not support \(BuiltinMacros.VALIDATE_HEADER_DEPENDENCIES.name)"))
     }
 
-    /// Compute missing module dependencies.
-    public func computeMissingAndUnusedDependencies(includes: [Path]) -> (missing: [HeaderDependency], unused: [HeaderDependency]) {
+    /// Compute missing header dependencies.
+    public func computeMissingAndUnusedDependencies(includes: [(Path, includeLocations: [Diagnostic.Location])]) -> (missing: [(HeaderDependency, includeLocations: [Diagnostic.Location])], unused: [HeaderDependency]) {
         let declaredNames = Set(declared.map { $0.name })
 
-        let missing: [HeaderDependency]
+        let missing: [(HeaderDependency, includeLocations: [Diagnostic.Location])]
         if validate != .no {
-            missing = includes.filter { file in
-                return !declaredNames.contains(where: { file.ends(with: $0) })
-            }.map {
+            missing = includes.filter { include in
+                return !declaredNames.contains(where: { include.0.ends(with: $0) })
+            }.map { include in
                 // TODO: What if the basename doesn't uniquely identify the header?
-                HeaderDependency(name: $0.basename, accessLevel: .Private, optional: false)
+                let dep = HeaderDependency(name: include.0.basename, accessLevel: .Private, optional: false)
+                return (dep, includeLocations: include.includeLocations)
             }
         }
         else {
@@ -334,15 +335,26 @@ public struct HeaderDependenciesContext: Sendable, SerializableCodable {
     ///
     /// The compiler tracing information does not provide the include locations or whether they are public imports
     /// (which depends on whether the import is in an installed header file).
-    public func makeDiagnostics(missingDependencies: [HeaderDependency], unusedDependencies: [HeaderDependency]) -> [Diagnostic] {
+    public func makeDiagnostics(missingDependencies: [(HeaderDependency, includeLocations: [Diagnostic.Location])], unusedDependencies: [HeaderDependency]) -> [Diagnostic] {
         let missingDiagnostics: [Diagnostic]
         if !missingDependencies.isEmpty {
             let behavior: Diagnostic.Behavior = validate == .yesError ? .error : .warning
 
-            let fixIt = fixItContext?.makeFixIt(newHeaders: missingDependencies)
+            let fixIt = fixItContext?.makeFixIt(newHeaders: missingDependencies.map { $0.0 })
             let fixIts = fixIt.map { [$0] } ?? []
 
-            let message = "Missing entries in \(BuiltinMacros.HEADER_DEPENDENCIES.name): \(missingDependencies.map { $0.asBuildSettingEntryQuotedIfNeeded }.sorted().joined(separator: " "))"
+            let importDiags: [Diagnostic] = missingDependencies
+                .flatMap { dep in
+                    dep.1.map {
+                        return Diagnostic(
+                            behavior: behavior,
+                            location: $0,
+                            data: DiagnosticData("Missing entry in \(BuiltinMacros.HEADER_DEPENDENCIES.name): \(dep.0.asBuildSettingEntryQuotedIfNeeded)"),
+                            fixIts: fixIts)
+                    }
+                }
+
+            let message = "Missing entries in \(BuiltinMacros.HEADER_DEPENDENCIES.name): \(missingDependencies.map { $0.0.asBuildSettingEntryQuotedIfNeeded }.sorted().joined(separator: " "))"
 
             let location: Diagnostic.Location = fixIt.map {
                 Diagnostic.Location.path($0.sourceRange.path, line: $0.sourceRange.endLine, column: $0.sourceRange.endColumn)
@@ -352,7 +364,8 @@ public struct HeaderDependenciesContext: Sendable, SerializableCodable {
                 behavior: behavior,
                 location: location,
                 data: DiagnosticData(message),
-                fixIts: fixIts)]
+                fixIts: fixIts,
+                childDiagnostics: importDiags)]
         }
         else {
             missingDiagnostics = []
diff --git a/Sources/SWBTaskExecution/TaskActions/ValidateDependenciesTaskAction.swift b/Sources/SWBTaskExecution/TaskActions/ValidateDependenciesTaskAction.swift
index dc4f94b6..45325d9f 100644
--- a/Sources/SWBTaskExecution/TaskActions/ValidateDependenciesTaskAction.swift
+++ b/Sources/SWBTaskExecution/TaskActions/ValidateDependenciesTaskAction.swift
@@ -116,7 +116,7 @@ public final class ValidateDependenciesTaskAction: TaskAction {
                 if unsupported {
                     diagnostics.append(contentsOf: [headerContext.makeUnsupportedToolchainDiagnostic()])
                 } else {
-                    let (missingDeps, unusedDeps) = headerContext.computeMissingAndUnusedDependencies(includes: allClangIncludes.map { $0.path })
+                    let (missingDeps, unusedDeps) = headerContext.computeMissingAndUnusedDependencies(includes: allClangIncludes.map { ($0.path, $0.includeLocations) })
                     outputDelegate.incrementCounter(.headerDependenciesMissing, by: missingDeps.count)
                     outputDelegate.incrementCounter(.headerDependenciesUnused, by: unusedDeps.count)
 
diff --git a/Tests/SWBBuildSystemTests/DependencyValidationTests.swift b/Tests/SWBBuildSystemTests/DependencyValidationTests.swift
index 64a753ca..4c32a8d9 100644
--- a/Tests/SWBBuildSystemTests/DependencyValidationTests.swift
+++ b/Tests/SWBBuildSystemTests/DependencyValidationTests.swift
@@ -660,17 +660,18 @@ fileprivate struct DependencyValidationTests: CoreBasedTests {
                         groupTree: TestGroup(
                             "Sources", path: "Sources",
                             children: [
-                                TestFile("CoreFoo.c")
+                                TestFile("CoreFoo.c"),
+                                TestFile("Project.xcconfig"),
                             ]),
                         buildConfigurations: [
                             TestBuildConfiguration(
                                 "Debug",
+                                baseConfig: "Project.xcconfig",
                                 buildSettings: [
                                     "PRODUCT_NAME": "$(TARGET_NAME)",
                                     "CLANG_ENABLE_MODULES": enableModules,
                                     "CLANG_ENABLE_EXPLICIT_MODULES": enableModules,
                                     "GENERATE_INFOPLIST_FILE": "YES",
-                                    "HEADER_DEPENDENCIES": "stdio.h",
                                     "VALIDATE_HEADER_DEPENDENCIES": "YES_ERROR",
                                     "SDKROOT": "$(HOST_PLATFORM)",
                                     "SUPPORTED_PLATFORMS": "$(HOST_PLATFORM)",
@@ -691,9 +692,10 @@ fileprivate struct DependencyValidationTests: CoreBasedTests {
 
             let tester = try await BuildOperationTester(getCore(), testWorkspace, simulated: false)
             let SRCROOT = testWorkspace.sourceRoot.join("aProject")
+            let srcFile = SRCROOT.join("Sources/CoreFoo.c")
 
             // Write the source files.
-            try await tester.fs.writeFileContents(SRCROOT.join("Sources/CoreFoo.c")) { contents in
+            try await tester.fs.writeFileContents(srcFile) { contents in
                 contents <<< """
                     #include <stdio.h>
                     #include <stdlib.h>
@@ -702,9 +704,41 @@ fileprivate struct DependencyValidationTests: CoreBasedTests {
                 """
             }
 
+            let projectXCConfigPath = SRCROOT.join("Sources/Project.xcconfig")
+            try await tester.fs.writeFileContents(projectXCConfigPath) { stream in
+                stream <<<
+            """
+            HEADER_DEPENDENCIES = stdio.h
+            """
+            }
+
             // Expect complaint about undeclared dependency
             try await tester.checkBuild(parameters: BuildParameters(configuration: "Debug"), runDestination: .host, persistent: true) { results in
-                results.checkError(.contains("Missing entries in HEADER_DEPENDENCIES: stdlib.h"))
+                results.checkError(.contains("Missing entries in HEADER_DEPENDENCIES: stdlib.h")) {
+                    diag in
+                    let expectedDiag = Diagnostic(
+                        behavior: .error,
+                        location: Diagnostic.Location.path(projectXCConfigPath, line: 1, column: 30),
+                        data: DiagnosticData("Missing entries in HEADER_DEPENDENCIES: stdlib.h"),
+                        fixIts: [
+                            Diagnostic.FixIt(
+                                sourceRange: Diagnostic.SourceRange(path: projectXCConfigPath, startLine: 1, startColumn: 30, endLine: 1, endColumn: 30),
+                                newText: " \\\n    stdlib.h"),
+                        ],
+                        childDiagnostics: [
+                            Diagnostic(
+                                behavior: .error,
+                                location: Diagnostic.Location.path(srcFile, line: 2, column: 8),
+                                data: DiagnosticData("Missing entry in HEADER_DEPENDENCIES: stdlib.h"),
+                                fixIts: [Diagnostic.FixIt(
+                                    sourceRange: Diagnostic.SourceRange(path: projectXCConfigPath, startLine: 1, startColumn: 30, endLine: 1, endColumn: 30),
+                                    newText: " \\\n    stdlib.h")],
+                            ),
+                        ]
+                    )
+                    #expect(expectedDiag == diag)
+                    return true
+                }
             }
 
             // Declaring dependencies resolves the problem