diff --git a/internal/terraform/node_resource_plan.go b/internal/terraform/node_resource_plan.go
index 5a01d9337dcf..1ee94c7435f0 100644
--- a/internal/terraform/node_resource_plan.go
+++ b/internal/terraform/node_resource_plan.go
@@ -38,6 +38,9 @@ type nodeExpandPlannableResource struct {
 
 	// We attach dependencies to the Resource during refresh, since the
 	// instances are instantiated during DynamicExpand.
+	// FIXME: These would be better off converted to a generic Set data
+	// structure in the future, as we need to compare for equality and take the
+	// union of multiple groups of dependencies.
 	dependencies []addrs.ConfigResource
 }
 
diff --git a/internal/terraform/node_resource_plan_instance.go b/internal/terraform/node_resource_plan_instance.go
index 46ca37f7de2c..14bded923aa3 100644
--- a/internal/terraform/node_resource_plan_instance.go
+++ b/internal/terraform/node_resource_plan_instance.go
@@ -391,6 +391,14 @@ func depsEqual(a, b []addrs.ConfigResource) bool {
 		return false
 	}
 
+	// Because we need to sort the deps to compare equality, make shallow
+	// copies to prevent concurrently modifying the array values on
+	// dependencies shared between expanded instances.
+	copyA, copyB := make([]addrs.ConfigResource, len(a)), make([]addrs.ConfigResource, len(b))
+	copy(copyA, a)
+	copy(copyB, b)
+	a, b = copyA, copyB
+
 	less := func(s []addrs.ConfigResource) func(i, j int) bool {
 		return func(i, j int) bool {
 			return s[i].String() < s[j].String()