diff --git a/modules/juce_audio_processors/format_types/juce_AudioUnitPluginFormat.mm b/modules/juce_audio_processors/format_types/juce_AudioUnitPluginFormat.mm
index 2eaa9da0a7..0c7b1c7df1 100644
--- a/modules/juce_audio_processors/format_types/juce_AudioUnitPluginFormat.mm
+++ b/modules/juce_audio_processors/format_types/juce_AudioUnitPluginFormat.mm
@@ -216,13 +216,40 @@ namespace AudioUnitFormatHelpers
                 if (manuString != nullptr && CFGetTypeID (manuString) == CFStringGetTypeID())
                     manufacturer = String::fromCFString ((CFStringRef) manuString);
 
-                const ResFileRefNum resFileId = CFBundleOpenBundleResourceMap (bundleRef.get());
-                UseResFile (resFileId);
+                class ScopedBundleResourceMap final
+                {
+                public:
+                    explicit ScopedBundleResourceMap (CFBundleRef refIn) : ref (refIn),
+                                                                           resFileId (CFBundleOpenBundleResourceMap (ref)),
+                                                                           valid (resFileId != -1)
+                    {
+                        if (valid)
+                            UseResFile (resFileId);
+                    }
+
+                    ~ScopedBundleResourceMap()
+                    {
+                        if (valid)
+                            CFBundleCloseBundleResourceMap (ref, resFileId);
+                    }
+
+                    bool isValid() const noexcept
+                    {
+                        return valid;
+                    }
+
+                private:
+                    const CFBundleRef ref;
+                    const ResFileRefNum resFileId;
+                    const bool valid;
+                };
+
+                const ScopedBundleResourceMap resourceMap { bundleRef.get() };
 
                 const OSType thngType = stringToOSType ("thng");
                 auto numResources = Count1Resources (thngType);
 
-                if (numResources > 0)
+                if (resourceMap.isValid() && numResources > 0)
                 {
                     for (ResourceIndex i = 1; i <= numResources; ++i)
                     {
@@ -268,8 +295,6 @@ namespace AudioUnitFormatHelpers
 
                     [bundle release];
                 }
-
-                CFBundleCloseBundleResourceMap (bundleRef.get(), resFileId);
             }
         }