diff --git a/forge/build.gradle b/forge/build.gradle
index 262aac78..5d783901 100644
--- a/forge/build.gradle
+++ b/forge/build.gradle
@@ -64,6 +64,7 @@ dependencies {
     modCompileOnly("team.chisel.ctm:CTM:${ctm_version}")
     modCompileOnly("curse.maven:supermartijncore-454372:4455378")
     modCompileOnly("curse.maven:valhesiastructures-347488:3476252")
+    modCompileOnly("curse.maven:sophbackpacks-422301:4167327")
     modCompileOnly files("deps/starlight-1.2.jar")
     modCompileOnly("appeng:appliedenergistics2:8.4.7")
     modCompileOnly("vazkii.patchouli:Patchouli:1.16.4-53.3")
diff --git a/forge/src/main/java/org/embeddedt/modernfix/forge/mixin/bugfix/unsafe_modded_shape_caches/BackpackShapesMixin.java b/forge/src/main/java/org/embeddedt/modernfix/forge/mixin/bugfix/unsafe_modded_shape_caches/BackpackShapesMixin.java
new file mode 100644
index 00000000..965adf2d
--- /dev/null
+++ b/forge/src/main/java/org/embeddedt/modernfix/forge/mixin/bugfix/unsafe_modded_shape_caches/BackpackShapesMixin.java
@@ -0,0 +1,24 @@
+package org.embeddedt.modernfix.forge.mixin.bugfix.unsafe_modded_shape_caches;
+
+import net.minecraft.world.phys.shapes.VoxelShape;
+import net.p3pp3rf1y.sophisticatedbackpacks.backpack.BackpackShapes;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Mutable;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+@Mixin(value = BackpackShapes.class, remap = false)
+public abstract class BackpackShapesMixin {
+    @Mutable @Shadow @Final private static Map<Integer, VoxelShape> SHAPES;
+
+    @Inject(method = "<clinit>", at = @At("RETURN"))
+    private static void concurrentMapInitialization(CallbackInfo ci) {
+        SHAPES = new ConcurrentHashMap<>(SHAPES);
+    }
+}
\ No newline at end of file