diff --git a/hclsyntax/expression.go b/hclsyntax/expression.go
index 94977460..f4c3a6d7 100644
--- a/hclsyntax/expression.go
+++ b/hclsyntax/expression.go
@@ -1430,9 +1430,9 @@ func (e *ForExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
 		})
 		return cty.DynamicVal, diags
 	}
-	if !collVal.IsKnown() {
-		return cty.DynamicVal, diags
-	}
+
+	// Grab the CondExpr marks when we're returning early with an unknown
+	var condMarks cty.ValueMarks
 
 	// Before we start we'll do an early check to see if any CondExpr we've
 	// been given is of the wrong type. This isn't 100% reliable (it may
@@ -1460,6 +1460,9 @@ func (e *ForExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
 			})
 			return cty.DynamicVal, diags
 		}
+
+		_, condMarks = result.Unmark()
+
 		_, err := convert.Convert(result, cty.Bool)
 		if err != nil {
 			diags = append(diags, &hcl.Diagnostic{
@@ -1478,6 +1481,10 @@ func (e *ForExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
 		}
 	}
 
+	if !collVal.IsKnown() {
+		return cty.DynamicVal.WithMarks(append(marks, condMarks)...), diags
+	}
+
 	if e.KeyExpr != nil {
 		// Producing an object
 		var vals map[string]cty.Value
@@ -1518,6 +1525,12 @@ func (e *ForExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
 					known = false
 					continue
 				}
+
+				// Extract and merge marks from the include expression into the
+				// main set of marks
+				_, includeMarks := includeRaw.Unmark()
+				marks = append(marks, includeMarks)
+
 				include, err := convert.Convert(includeRaw, cty.Bool)
 				if err != nil {
 					if known {
@@ -1541,7 +1554,7 @@ func (e *ForExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
 
 				// Extract and merge marks from the include expression into the
 				// main set of marks
-				includeUnmarked, includeMarks := include.Unmark()
+				includeUnmarked, _ := include.Unmark()
 				marks = append(marks, includeMarks)
 				if includeUnmarked.False() {
 					// Skip this element
@@ -1566,6 +1579,10 @@ func (e *ForExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
 				known = false
 				continue
 			}
+
+			_, keyMarks := keyRaw.Unmark()
+			marks = append(marks, keyMarks)
+
 			if !keyRaw.IsKnown() {
 				known = false
 				continue
@@ -1588,8 +1605,7 @@ func (e *ForExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
 				continue
 			}
 
-			key, keyMarks := key.Unmark()
-			marks = append(marks, keyMarks)
+			key, _ = key.Unmark()
 
 			val, valDiags := e.ValExpr.Value(childCtx)
 			diags = append(diags, valDiags...)
@@ -1619,7 +1635,7 @@ func (e *ForExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
 		}
 
 		if !known {
-			return cty.DynamicVal, diags
+			return cty.DynamicVal.WithMarks(marks...), diags
 		}
 
 		if e.Group {
@@ -1665,6 +1681,12 @@ func (e *ForExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
 					known = false
 					continue
 				}
+
+				// Extract and merge marks from the include expression into the
+				// main set of marks
+				_, includeMarks := includeRaw.Unmark()
+				marks = append(marks, includeMarks)
+
 				if !includeRaw.IsKnown() {
 					// We will eventually return DynamicVal, but we'll continue
 					// iterating in case there are other diagnostics to gather
@@ -1690,10 +1712,7 @@ func (e *ForExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
 					continue
 				}
 
-				// Extract and merge marks from the include expression into the
-				// main set of marks
-				includeUnmarked, includeMarks := include.Unmark()
-				marks = append(marks, includeMarks)
+				includeUnmarked, _ := include.Unmark()
 				if includeUnmarked.False() {
 					// Skip this element
 					continue
@@ -1706,7 +1725,7 @@ func (e *ForExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
 		}
 
 		if !known {
-			return cty.DynamicVal, diags
+			return cty.DynamicVal.WithMarks(marks...), diags
 		}
 
 		return cty.TupleVal(vals).WithMarks(marks...), diags
diff --git a/hclsyntax/expression_test.go b/hclsyntax/expression_test.go
index cb1132e3..df11d28c 100644
--- a/hclsyntax/expression_test.go
+++ b/hclsyntax/expression_test.go
@@ -1143,6 +1143,49 @@ upper(
 			}).Mark("sensitive"),
 			0,
 		},
+		{
+			`{ for k, v in things: k => v if k != unknown_secret }`,
+			&hcl.EvalContext{
+				Variables: map[string]cty.Value{
+					"things": cty.MapVal(map[string]cty.Value{
+						"a": cty.True,
+						"b": cty.False,
+						"c": cty.False,
+					}),
+					"unknown_secret": cty.UnknownVal(cty.String).Mark("sensitive"),
+				},
+			},
+			cty.DynamicVal.Mark("sensitive"),
+			0,
+		},
+		{
+			`[ for v in things: v if v != unknown_secret ]`,
+			&hcl.EvalContext{
+				Variables: map[string]cty.Value{
+					"things": cty.TupleVal([]cty.Value{
+						cty.StringVal("a"),
+						cty.StringVal("b"),
+					}),
+					"unknown_secret": cty.UnknownVal(cty.String).Mark("sensitive"),
+				},
+			},
+			cty.DynamicVal.Mark("sensitive"),
+			0,
+		},
+		{
+			`[ for v in things: v if v != secret ]`,
+			&hcl.EvalContext{
+				Variables: map[string]cty.Value{
+					"things": cty.TupleVal([]cty.Value{
+						cty.UnknownVal(cty.String).Mark("mark"),
+						cty.StringVal("b"),
+					}),
+					"secret": cty.StringVal("b").Mark("sensitive"),
+				},
+			},
+			cty.DynamicVal.WithMarks(cty.NewValueMarks("mark", "sensitive")),
+			0,
+		},
 		{
 			`[{name: "Steve"}, {name: "Ermintrude"}].*.name`,
 			nil,