diff --git a/terraform/context_validate_test.go b/terraform/context_validate_test.go
index 8b380ba03f..178f291746 100644
--- a/terraform/context_validate_test.go
+++ b/terraform/context_validate_test.go
@@ -1435,7 +1435,7 @@ resource "aws_instance" "foo" {
 module "nested" {
   count = 2
   source = "./nested"
-  input = 2
+  input = count.index
 }
 `,
 		"mod/nested/main.tf": `
diff --git a/terraform/eval_variable.go b/terraform/eval_variable.go
index e5ff7cdf74..5fc90245b5 100644
--- a/terraform/eval_variable.go
+++ b/terraform/eval_variable.go
@@ -8,6 +8,7 @@ import (
 	"github.com/hashicorp/hcl/v2"
 	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/configs"
+	"github.com/hashicorp/terraform/instances"
 	"github.com/hashicorp/terraform/tfdiags"
 	"github.com/zclconf/go-cty/cty"
 	"github.com/zclconf/go-cty/cty/convert"
@@ -42,12 +43,12 @@ type EvalModuleCallArgument struct {
 	Expr           hcl.Expression
 	ModuleInstance addrs.ModuleInstance
 
-	// If this flag is set, any diagnostics are discarded and this operation
-	// will always succeed, though may produce an unknown value in the
-	// event of an error.
-	IgnoreDiagnostics bool
-
 	Values map[string]cty.Value
+
+	// validateOnly indicates that this evaluation is only for config
+	// validation, and we will not have any expansion module instance
+	// repetition data.
+	validateOnly bool
 }
 
 func (n *EvalModuleCallArgument) Eval(ctx EvalContext) (interface{}, error) {
@@ -69,9 +70,24 @@ func (n *EvalModuleCallArgument) Eval(ctx EvalContext) (interface{}, error) {
 		return nil, nil
 	}
 
-	// Get the repetition data for this module instance,
-	// so we can create the appropriate scope for evaluating our expression
-	moduleInstanceRepetitionData := ctx.InstanceExpander().GetModuleInstanceRepetitionData(n.ModuleInstance)
+	var moduleInstanceRepetitionData instances.RepetitionData
+
+	switch {
+	case n.validateOnly:
+		// the instance expander does not track unknown expansion values, so we
+		// have to assume all RepetitionData is unknown.
+		moduleInstanceRepetitionData = instances.RepetitionData{
+			CountIndex: cty.UnknownVal(cty.Number),
+			EachKey:    cty.UnknownVal(cty.String),
+			EachValue:  cty.DynamicVal,
+		}
+
+	default:
+		// Get the repetition data for this module instance,
+		// so we can create the appropriate scope for evaluating our expression
+		moduleInstanceRepetitionData = ctx.InstanceExpander().GetModuleInstanceRepetitionData(n.ModuleInstance)
+	}
+
 	scope := ctx.EvaluationScope(nil, moduleInstanceRepetitionData)
 	val, diags := scope.EvalExpr(expr, cty.DynamicPseudoType)
 
@@ -96,9 +112,6 @@ func (n *EvalModuleCallArgument) Eval(ctx EvalContext) (interface{}, error) {
 	}
 
 	n.Values[name] = val
-	if n.IgnoreDiagnostics {
-		return nil, nil
-	}
 	return nil, diags.ErrWithWarnings()
 }
 
@@ -116,15 +129,10 @@ type evalVariableValidations struct {
 	// This will be nil for root module variables, because their values come
 	// from outside the configuration.
 	Expr hcl.Expression
-
-	// If this flag is set, this node becomes a no-op.
-	// This is here for consistency with EvalModuleCallArgument so that it
-	// can be populated with the same value, where needed.
-	IgnoreDiagnostics bool
 }
 
 func (n *evalVariableValidations) Eval(ctx EvalContext) (interface{}, error) {
-	if n.Config == nil || n.IgnoreDiagnostics || len(n.Config.Validations) == 0 {
+	if n.Config == nil || len(n.Config.Validations) == 0 {
 		log.Printf("[TRACE] evalVariableValidations: not active for %s, so skipping", n.Addr)
 		return nil, nil
 	}
diff --git a/terraform/node_module_variable.go b/terraform/node_module_variable.go
index 53543b47fc..62ebb19132 100644
--- a/terraform/node_module_variable.go
+++ b/terraform/node_module_variable.go
@@ -11,8 +11,6 @@ import (
 	"github.com/zclconf/go-cty/cty"
 )
 
-type ConcreteVariableNodeFunc func(n *nodeExpandModuleVariable) dag.Vertex
-
 // nodeExpandModuleVariable is the placeholder for an variable that has not yet had
 // its module path expanded.
 type nodeExpandModuleVariable struct {
@@ -176,15 +174,25 @@ func (n *nodeModuleVariable) EvalTree() EvalNode {
 		Nodes: []EvalNode{
 			&EvalOpFilter{
 				Ops: []walkOperation{walkRefresh, walkPlan, walkApply,
-					walkDestroy, walkValidate},
+					walkDestroy},
 				Node: &EvalModuleCallArgument{
 					Addr:           n.Addr.Variable,
 					Config:         n.Config,
 					Expr:           n.Expr,
 					ModuleInstance: n.ModuleInstance,
 					Values:         vals,
+				},
+			},
 
-					IgnoreDiagnostics: false,
+			&EvalOpFilter{
+				Ops: []walkOperation{walkValidate},
+				Node: &EvalModuleCallArgument{
+					Addr:           n.Addr.Variable,
+					Config:         n.Config,
+					Expr:           n.Expr,
+					ModuleInstance: n.ModuleInstance,
+					Values:         vals,
+					validateOnly:   true,
 				},
 			},
 
@@ -197,8 +205,6 @@ func (n *nodeModuleVariable) EvalTree() EvalNode {
 				Addr:   n.Addr,
 				Config: n.Config,
 				Expr:   n.Expr,
-
-				IgnoreDiagnostics: false,
 			},
 		},
 	}
diff --git a/terraform/node_root_variable.go b/terraform/node_root_variable.go
index 9740bf4ebf..f9814f375a 100644
--- a/terraform/node_root_variable.go
+++ b/terraform/node_root_variable.go
@@ -50,8 +50,6 @@ func (n *NodeRootVariable) EvalTree() EvalNode {
 		Addr:   addrs.RootModuleInstance.InputVariable(n.Addr.Name),
 		Config: n.Config,
 		Expr:   nil, // not set for root module variables
-
-		IgnoreDiagnostics: false,
 	}
 }
 
diff --git a/terraform/transform_module_variable.go b/terraform/transform_module_variable.go
index 1d74ba3327..99a86c01d9 100644
--- a/terraform/transform_module_variable.go
+++ b/terraform/transform_module_variable.go
@@ -113,7 +113,6 @@ func (t *ModuleVariableTransformer) transformSingle(g *Graph, parent, c *configs
 			Config: v,
 			Expr:   expr,
 		}
-
 		g.Add(node)
 	}