diff --git a/src/object.di b/src/object.di
index f1e6a951013..2d92e873c61 100644
--- a/src/object.di
+++ b/src/object.di
@@ -279,6 +279,17 @@ struct ModuleInfo
     uint _flags;
     uint _index;
 
+    version (all)
+    {
+        deprecated("ModuleInfo cannot be copy-assigned because it is a variable-sized struct.")
+        void opAssign(in ModuleInfo m) { _flags = m._flags; _index = m._index; }
+    }
+    else
+    {
+        @disable this();
+        @disable this(this) const;
+    }
+
 const:
     @property uint index() nothrow pure;
     @property uint flags() nothrow pure;
@@ -293,7 +304,7 @@ const:
     @property TypeInfo_Class[] localClasses() nothrow pure;
     @property string name() nothrow pure;
 
-    static int opApply(scope int delegate(immutable(ModuleInfo*)) dg);
+    static int opApply(scope int delegate(ModuleInfo*) dg);
 }
 
 class Throwable : Object
diff --git a/src/object_.d b/src/object_.d
index 09f8e86fe29..f8770794da4 100644
--- a/src/object_.d
+++ b/src/object_.d
@@ -1591,6 +1591,17 @@ struct ModuleInfo
     uint _flags;
     uint _index; // index into _moduleinfo_array[]
 
+    version (all)
+    {
+        deprecated("ModuleInfo cannot be copy-assigned because it is a variable-sized struct.")
+        void opAssign(in ModuleInfo m) { _flags = m._flags; _index = m._index; }
+    }
+    else
+    {
+        @disable this();
+        @disable this(this) const;
+    }
+
 const:
     private void* addrOf(int flag) nothrow pure
     in
@@ -1724,20 +1735,21 @@ const:
         // return null;
     }
 
-    static int opApply(scope int delegate(immutable(ModuleInfo*)) dg)
+    static int opApply(scope int delegate(ModuleInfo*) dg)
     {
         import rt.minfo;
-        return rt.minfo.moduleinfos_apply(dg);
+        // Bugzilla 13084 - enforcing immutable ModuleInfo would break client code
+        return rt.minfo.moduleinfos_apply(
+            (immutable(ModuleInfo*)m) => dg(cast(ModuleInfo*)m));
     }
 }
 
 unittest
 {
-    ModuleInfo mi;
+    ModuleInfo* m1;
     foreach (m; ModuleInfo)
     {
-        mi = *m;
-        break;
+        m1 = m;
     }
 }
 
diff --git a/src/rt/minfo.d b/src/rt/minfo.d
index 865130c52da..e185447d5bf 100644
--- a/src/rt/minfo.d
+++ b/src/rt/minfo.d
@@ -392,6 +392,11 @@ unittest
 
     static struct UTModuleInfo
     {
+        this(uint flags)
+        {
+            mi._flags = flags;
+        }
+
         void setImports(immutable(ModuleInfo)*[] imports...)
         {
             import core.bitop;
@@ -413,7 +418,7 @@ unittest
 
     static UTModuleInfo mockMI(uint flags)
     {
-        auto mi = UTModuleInfo(ModuleInfo(flags | MIimportedModules));
+        auto mi = UTModuleInfo(flags | MIimportedModules);
         auto p = cast(void function()*)&mi.pad;
         if (flags & MItlsctor) *p++ = &stub;
         if (flags & MItlsdtor) *p++ = &stub;
diff --git a/src/test_runner.d b/src/test_runner.d
index 03d19970791..e5c66483ea1 100644
--- a/src/test_runner.d
+++ b/src/test_runner.d
@@ -1,7 +1,7 @@
 import core.runtime, core.time : TickDuration;
 import core.stdc.stdio;
 
-immutable(ModuleInfo*) getModuleInfo(string name)
+ModuleInfo* getModuleInfo(string name)
 {
     foreach (m; ModuleInfo)
         if (m.name == name) return m;