diff --git a/terraform/eval_interpolate.go b/terraform/eval_interpolate.go
index 6825ff590..df3bcb98e 100644
--- a/terraform/eval_interpolate.go
+++ b/terraform/eval_interpolate.go
@@ -1,6 +1,10 @@
 package terraform
 
-import "github.com/hashicorp/terraform/config"
+import (
+	"log"
+
+	"github.com/hashicorp/terraform/config"
+)
 
 // EvalInterpolate is an EvalNode implementation that takes a raw
 // configuration and interpolates it.
@@ -22,3 +26,28 @@ func (n *EvalInterpolate) Eval(ctx EvalContext) (interface{}, error) {
 
 	return nil, nil
 }
+
+// EvalTryInterpolate is an EvalNode implementation that takes a raw
+// configuration and interpolates it, but only logs a warning on an
+// interpolation error, and stops further Eval steps.
+// This is used during Input where a value may not be known before Refresh, but
+// we don't want to block Input.
+type EvalTryInterpolate struct {
+	Config   *config.RawConfig
+	Resource *Resource
+	Output   **ResourceConfig
+}
+
+func (n *EvalTryInterpolate) Eval(ctx EvalContext) (interface{}, error) {
+	rc, err := ctx.Interpolate(n.Config, n.Resource)
+	if err != nil {
+		log.Printf("[WARN] Interpolation %q failed: %s", n.Config.Key, err)
+		return nil, EvalEarlyExitError{}
+	}
+
+	if n.Output != nil {
+		*n.Output = rc
+	}
+
+	return nil, nil
+}
diff --git a/terraform/eval_state.go b/terraform/eval_state.go
index 126a0e63a..1f67e3d86 100644
--- a/terraform/eval_state.go
+++ b/terraform/eval_state.go
@@ -1,6 +1,8 @@
 package terraform
 
-import "fmt"
+import (
+	"fmt"
+)
 
 // EvalReadState is an EvalNode implementation that reads the
 // primary InstanceState for a specific resource out of the state.
diff --git a/terraform/graph_builder_input.go b/terraform/graph_builder_input.go
index 0df48cdb8..10fd8b1e9 100644
--- a/terraform/graph_builder_input.go
+++ b/terraform/graph_builder_input.go
@@ -10,6 +10,9 @@ import (
 // and is based on the PlanGraphBuilder. The PlanGraphBuilder passed in will be
 // modified and should not be used for any other operations.
 func InputGraphBuilder(p *PlanGraphBuilder) GraphBuilder {
+	// convert this to an InputPlan
+	p.Input = true
+
 	// We're going to customize the concrete functions
 	p.CustomConcrete = true
 
diff --git a/terraform/graph_builder_plan.go b/terraform/graph_builder_plan.go
index 4b29bbb4b..9c7e4c1db 100644
--- a/terraform/graph_builder_plan.go
+++ b/terraform/graph_builder_plan.go
@@ -40,6 +40,9 @@ type PlanGraphBuilder struct {
 	// Validate will do structural validation of the graph.
 	Validate bool
 
+	// Input represents that this builder is for an Input operation.
+	Input bool
+
 	// CustomConcrete can be set to customize the node types created
 	// for various parts of the plan. This is useful in order to customize
 	// the plan behavior.
@@ -107,7 +110,10 @@ func (b *PlanGraphBuilder) Steps() []GraphTransformer {
 		),
 
 		// Add module variables
-		&ModuleVariableTransformer{Module: b.Module},
+		&ModuleVariableTransformer{
+			Module: b.Module,
+			Input:  b.Input,
+		},
 
 		// Connect so that the references are ready for targeting. We'll
 		// have to connect again later for providers and so on.
diff --git a/terraform/node_module_variable.go b/terraform/node_module_variable.go
index 13fe8fc3a..63b84a9c5 100644
--- a/terraform/node_module_variable.go
+++ b/terraform/node_module_variable.go
@@ -15,6 +15,9 @@ type NodeApplyableModuleVariable struct {
 	Value     *config.RawConfig // Value is the value that is set
 
 	Module *module.Tree // Antiquated, want to remove
+
+	// Input is set if this graph was created for the Input operation.
+	Input bool
 }
 
 func (n *NodeApplyableModuleVariable) Name() string {
@@ -92,12 +95,24 @@ func (n *NodeApplyableModuleVariable) EvalTree() EvalNode {
 	// within the variables mapping.
 	var config *ResourceConfig
 	variables := make(map[string]interface{})
+
+	var interpolate EvalNode
+
+	if n.Input {
+		interpolate = &EvalTryInterpolate{
+			Config: n.Value,
+			Output: &config,
+		}
+	} else {
+		interpolate = &EvalInterpolate{
+			Config: n.Value,
+			Output: &config,
+		}
+	}
+
 	return &EvalSequence{
 		Nodes: []EvalNode{
-			&EvalInterpolate{
-				Config: n.Value,
-				Output: &config,
-			},
+			interpolate,
 
 			&EvalVariableBlock{
 				Config:         &config,
diff --git a/terraform/transform_module_variable.go b/terraform/transform_module_variable.go
index 467950bdc..dbfd16871 100644
--- a/terraform/transform_module_variable.go
+++ b/terraform/transform_module_variable.go
@@ -17,6 +17,7 @@ type ModuleVariableTransformer struct {
 	Module *module.Tree
 
 	DisablePrune bool // True if pruning unreferenced should be disabled
+	Input        bool // True if this is from an Input operation.
 }
 
 func (t *ModuleVariableTransformer) Transform(g *Graph) error {
@@ -99,6 +100,7 @@ func (t *ModuleVariableTransformer) transformSingle(g *Graph, parent, m *module.
 			Config:    v,
 			Value:     value,
 			Module:    t.Module,
+			Input:     t.Input,
 		}
 
 		if !t.DisablePrune {