diff --git a/.structural.yml b/.structural.yml
new file mode 100644
index 00000000..1c097481
--- /dev/null
+++ b/.structural.yml
@@ -0,0 +1,15 @@
+# Copyright Ion Fusion contributors. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+packages:
+    - "dev.ionfusion.fusion"
+    - "dev.ionfusion.runtime.base"
+    - "dev.ionfusion.runtime.embed"
+
+rules:
+    # For each package, declare other packages it can depend on.
+    "dev.ionfusion.fusion":
+        - "dev.ionfusion.runtime.base"
+        - "dev.ionfusion.runtime.embed"
+    "dev.ionfusion.runtime.embed":
+        - "dev.ionfusion.runtime.base"
diff --git a/runtime/build.gradle.kts b/runtime/build.gradle.kts
index 51c29a6d..3699aff7 100644
--- a/runtime/build.gradle.kts
+++ b/runtime/build.gradle.kts
@@ -5,6 +5,7 @@ plugins {
     id("buildlogic.fusion-common-conventions")
     id("buildlogic.java-library-conventions")
     id("buildlogic.jacoco-conventions")
+    id("com.adrianczuczka.structural")
 }
 
 dependencies {
@@ -77,6 +78,13 @@ tasks.jacocoTestCoverageVerification {
 }
 
 
+structural {
+    // Plugin (@1.1.4) resolves this relative to the root directory, not this project.
+    // https://github.com/adrianczuczka/structural/issues/5
+    config = ".structural.yml"
+}
+
+
 //=============================================================================
 // Documentation
 
diff --git a/settings.gradle.kts b/settings.gradle.kts
index 157cf469..0d618ad1 100644
--- a/settings.gradle.kts
+++ b/settings.gradle.kts
@@ -12,4 +12,15 @@
 // Among other things, this becomes the module name in IDEA.
 rootProject.name = "fusion-java"
 
+pluginManagement {
+    repositories {
+        mavenCentral()
+    }
+    plugins {
+        // Enforce our desired inter-package dependency structure.
+        // https://github.com/adrianczuczka/structural
+        id("com.adrianczuczka.structural") version "1.1.4"
+    }
+}
+
 include("testing", "runtime", "fusioncli", "sdk")