diff --git a/command/format/diff.go b/command/format/diff.go
index e80c7c637b..260c031dee 100644
--- a/command/format/diff.go
+++ b/command/format/diff.go
@@ -856,6 +856,10 @@ func ctyGetAttrMaybeNull(val cty.Value, name string) cty.Value {
 }
 
 func ctyCollectionValues(val cty.Value) []cty.Value {
+	if !val.IsKnown() {
+		return nil
+	}
+
 	ret := make([]cty.Value, 0, val.LengthInt())
 	for it := val.ElementIterator(); it.Next(); {
 		_, value := it.Element()
diff --git a/lang/funcs/collection.go b/lang/funcs/collection.go
index 68c2e12ee9..742b84c9eb 100644
--- a/lang/funcs/collection.go
+++ b/lang/funcs/collection.go
@@ -58,6 +58,11 @@ var ElementFunc = function.New(&function.Spec{
 			// can't happen because we checked this in the Type function above
 			return cty.DynamicVal, fmt.Errorf("invalid index: %s", err)
 		}
+
+		if !args[0].IsKnown() {
+			return cty.UnknownVal(retType), nil
+		}
+
 		l := args[0].LengthInt()
 		if l == 0 {
 			return cty.DynamicVal, fmt.Errorf("cannot use element function with an empty list")
@@ -251,6 +256,10 @@ var IndexFunc = function.New(&function.Spec{
 			return cty.NilVal, fmt.Errorf("argument must be a list or tuple")
 		}
 
+		if !args[0].IsKnown() {
+			return cty.UnknownVal(cty.Number), nil
+		}
+
 		if args[0].LengthInt() == 0 { // Easy path
 			return cty.NilVal, fmt.Errorf("cannot search an empty list")
 		}
@@ -666,6 +675,9 @@ var MatchkeysFunc = function.New(&function.Spec{
 		return args[0].Type(), nil
 	},
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
+		if !args[0].IsKnown() {
+			return cty.UnknownVal(cty.List(retType.ElementType())), nil
+		}
 
 		if args[0].LengthInt() != args[1].LengthInt() {
 			return cty.ListValEmpty(retType.ElementType()), fmt.Errorf("length of keys and values should be equal")
@@ -885,14 +897,14 @@ var ValuesFunc = function.New(&function.Spec{
 	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
 		mapVar := args[0]
 
-		if mapVar.LengthInt() == 0 {
-			return cty.ListValEmpty(retType.ElementType()), nil
-		}
-
 		if !mapVar.IsWhollyKnown() {
 			return cty.UnknownVal(retType), nil
 		}
 
+		if mapVar.LengthInt() == 0 {
+			return cty.ListValEmpty(retType.ElementType()), nil
+		}
+
 		keys, err := Keys(mapVar)
 		if err != nil {
 			return cty.NilVal, err
@@ -941,7 +953,7 @@ var ZipmapFunc = function.New(&function.Spec{
 		keys := args[0]
 		values := args[1]
 
-		if keys.LengthInt() == 0 {
+		if !keys.IsKnown() || !values.IsKnown() || keys.LengthInt() == 0 {
 			return cty.Map(cty.DynamicPseudoType), nil
 		}
 
@@ -955,7 +967,7 @@ var ZipmapFunc = function.New(&function.Spec{
 		keys := args[0]
 		values := args[1]
 
-		if keys.LengthInt() == 0 {
+		if !keys.IsKnown() || !values.IsKnown() || keys.LengthInt() == 0 {
 			return cty.MapValEmpty(cty.DynamicPseudoType), nil
 		}
 
diff --git a/plans/objchange/compatible.go b/plans/objchange/compatible.go
index 9298dc48e3..83b717554d 100644
--- a/plans/objchange/compatible.go
+++ b/plans/objchange/compatible.go
@@ -64,7 +64,7 @@ func assertObjectCompatible(schema *configschema.Block, planned, actual cty.Valu
 				return errs
 			}
 		case configschema.NestingList, configschema.NestingMap, configschema.NestingSet:
-			if plannedV.LengthInt() == 1 {
+			if plannedV.IsKnown() && plannedV.LengthInt() == 1 {
 				elemVs := plannedV.AsValueSlice()
 				if allLeafValuesUnknown(elemVs[0]) {
 					return errs
@@ -84,6 +84,10 @@ func assertObjectCompatible(schema *configschema.Block, planned, actual cty.Valu
 			// whether there are dynamically-typed attributes inside. However,
 			// both support a similar-enough API that we can treat them the
 			// same for our purposes here.
+			if !plannedV.IsKnown() {
+				continue
+			}
+
 			plannedL := plannedV.LengthInt()
 			actualL := actualV.LengthInt()
 			if plannedL != actualL {
@@ -125,6 +129,9 @@ func assertObjectCompatible(schema *configschema.Block, planned, actual cty.Valu
 					}
 				}
 			} else {
+				if !plannedV.IsKnown() {
+					continue
+				}
 				plannedL := plannedV.LengthInt()
 				actualL := actualV.LengthInt()
 				if plannedL != actualL {
@@ -146,6 +153,9 @@ func assertObjectCompatible(schema *configschema.Block, planned, actual cty.Valu
 			// content is also their key, and so we have no way to correlate
 			// them. Because of this, we simply verify that we still have the
 			// same number of elements.
+			if !plannedV.IsKnown() {
+				continue
+			}
 			plannedL := plannedV.LengthInt()
 			actualL := actualV.LengthInt()
 			if plannedL < actualL {
@@ -241,10 +251,12 @@ func assertValueCompatible(planned, actual cty.Value, path cty.Path) []error {
 		// so we can't correlate them properly. However, we will at least check
 		// to ensure that the number of elements is consistent, along with
 		// the general type-match checks we ran earlier in this function.
-		plannedL := planned.LengthInt()
-		actualL := actual.LengthInt()
-		if plannedL < actualL {
-			errs = append(errs, path.NewErrorf("length changed from %d to %d", plannedL, actualL))
+		if planned.IsKnown() {
+			plannedL := planned.LengthInt()
+			actualL := actual.LengthInt()
+			if plannedL < actualL {
+				errs = append(errs, path.NewErrorf("length changed from %d to %d", plannedL, actualL))
+			}
 		}
 	}
 
diff --git a/terraform/resource.go b/terraform/resource.go
index d1941739b7..9db0f2ab4a 100644
--- a/terraform/resource.go
+++ b/terraform/resource.go
@@ -276,6 +276,10 @@ func newResourceConfigShimmedComputedKeys(obj cty.Value, schema *configschema.Bl
 		}
 
 		blockVal := obj.GetAttr(typeName)
+		if !blockVal.IsKnown() {
+			continue
+		}
+
 		switch blockS.Nesting {
 		case configschema.NestingSingle:
 			keys := newResourceConfigShimmedComputedKeys(blockVal, &blockS.Block, fmt.Sprintf("%s%s.", prefix, typeName))