diff --git a/CHANGELOG.md b/CHANGELOG.md
index 61e6833423..221457913e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@ BUG FIXES:
 - When assigning an empty map to a variable that is declared as a map of an object type with at least one optional attribute, OpenTofu will no longer create a subtly-broken value. ([#2371](https://github.com/opentofu/opentofu/pull/2371))
 - The `format` and `formatlist` functions can now accept `null` as one of the arguments without causing problems during the apply phase. Previously these functions would incorrectly return an unknown value when given `null` and so could cause a failure during the apply phase where no unknown values are allowed. ([#2371](https://github.com/opentofu/opentofu/pull/2371))
 - Provider used in import is correctly identified. ([#2336](https://github.com/opentofu/opentofu/pull/2336))
+- `plantimestamp()` now returns unknown value during validation ([#2397](https://github.com/opentofu/opentofu/issues/2397))
 
 ## Previous Releases
 
diff --git a/internal/lang/funcs/datetime.go b/internal/lang/funcs/datetime.go
index 2f3b44ea3f..51c732999d 100644
--- a/internal/lang/funcs/datetime.go
+++ b/internal/lang/funcs/datetime.go
@@ -30,6 +30,11 @@ func MakeStaticTimestampFunc(static time.Time) function.Function {
 		Params: []function.Parameter{},
 		Type:   function.StaticReturnType(cty.String),
 		Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
+			// During validation phase, the planTimestamp is zero. By returning unknown value, it's forcing the
+			// HCL parser to skip any evaluation of other expressions that could use this.
+			if static.IsZero() {
+				return cty.UnknownVal(cty.String), nil
+			}
 			return cty.StringVal(static.Format(time.RFC3339)), nil
 		},
 	})
diff --git a/internal/lang/funcs/datetime_test.go b/internal/lang/funcs/datetime_test.go
index 9f2813eb02..2149ec2a63 100644
--- a/internal/lang/funcs/datetime_test.go
+++ b/internal/lang/funcs/datetime_test.go
@@ -185,3 +185,49 @@ func TestTimeCmp(t *testing.T) {
 		})
 	}
 }
+
+func TestMakeStaticTimestampFunc(t *testing.T) {
+	tests := []struct {
+		Name string
+		// Setup made like this to bind the generated time value to the wanted value.
+		Setup func() (time.Time, cty.Value)
+	}{
+		{
+			Name: "zero",
+			Setup: func() (time.Time, cty.Value) {
+				in := time.Time{}
+				out := cty.UnknownVal(cty.String)
+				return in, out
+			},
+		},
+		{
+			Name: "now",
+			Setup: func() (time.Time, cty.Value) {
+				in := time.Now()
+				out := cty.StringVal(in.Format(time.RFC3339))
+				return in, out
+			},
+		},
+		{
+			Name: "one year later",
+			Setup: func() (time.Time, cty.Value) {
+				in := time.Now().Add(8766 * time.Hour) // 1 year later
+				out := cty.StringVal(in.Format(time.RFC3339))
+				return in, out
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("MakeStaticTimestampFunc(%s)", test.Name), func(t *testing.T) {
+			in, want := test.Setup()
+			got, err := MakeStaticTimestampFunc(in).Call(nil)
+			if err != nil {
+				t.Fatalf("MakeStaticTimestampFunc is not meant to return error but got one: %v", err)
+			}
+			if !got.RawEquals(want) {
+				t.Errorf("wrong result\ngot:  %#v\nwant: %#v", got, want)
+			}
+		})
+	}
+}
diff --git a/internal/tofu/context_validate_test.go b/internal/tofu/context_validate_test.go
index 4786d2f830..fdc2067647 100644
--- a/internal/tofu/context_validate_test.go
+++ b/internal/tofu/context_validate_test.go
@@ -2488,3 +2488,21 @@ locals {
 		t.Fatalf("expected deprecated warning, got: %q\n", warn)
 	}
 }
+
+// Ensure that the plantimestamp() call is not affecting the validation step.
+func TestContext2Validate_rangeOverZeroPlanTimestamp(t *testing.T) {
+	p := testProvider("test")
+
+	m := testModule(t, "plan_range_over_plan_timestamp")
+
+	ctx := testContext2(t, &ContextOpts{
+		Providers: map[addrs.Provider]providers.Factory{
+			addrs.NewDefaultProvider("test"): testProviderFuncFixed(p),
+		},
+	})
+
+	diags := ctx.Validate(context.Background(), m)
+	if diags.HasErrors() {
+		t.Fatal(diags.ErrWithWarnings())
+	}
+}
diff --git a/internal/tofu/testdata/plan_range_over_plan_timestamp/main.tf b/internal/tofu/testdata/plan_range_over_plan_timestamp/main.tf
new file mode 100644
index 0000000000..b4aad009bf
--- /dev/null
+++ b/internal/tofu/testdata/plan_range_over_plan_timestamp/main.tf
@@ -0,0 +1,12 @@
+locals {
+  first_year = 2024
+  current_timestamp = plantimestamp()
+}
+
+output "table_years" {
+  value = toset(
+    [
+      for year in range(local.first_year, tonumber(formatdate("YYYY", local.current_timestamp)) + 2) : tostring(year)
+    ]
+  )
+}