diff --git a/.changes/v1.15/BUG FIXES-20260427-092612.yaml b/.changes/v1.15/BUG FIXES-20260427-092612.yaml
new file mode 100644
index 0000000000..644c047ec0
--- /dev/null
+++ b/.changes/v1.15/BUG FIXES-20260427-092612.yaml	
@@ -0,0 +1,5 @@
+kind: BUG FIXES
+body: Fixed crash when configuration has an invalid `action_trigger` nested block in `data` or `ephemeral` lifecycle blocks
+time: 2026-04-27T09:26:12.662049-04:00
+custom:
+    Issue: "38402"
diff --git a/internal/configs/resource.go b/internal/configs/resource.go
index 8f4276a61b..4d7569a115 100644
--- a/internal/configs/resource.go
+++ b/internal/configs/resource.go
@@ -509,6 +509,13 @@ func decodeEphemeralBlock(block *hcl.Block, override bool) (*Resource, hcl.Diagn
 					case "postcondition":
 						r.Postconditions = append(r.Postconditions, cr)
 					}
+				case "action_trigger":
+					diags = append(diags, &hcl.Diagnostic{
+						Severity: hcl.DiagError,
+						Summary:  "Invalid ephemeral resource lifecycle nested block",
+						Detail:   fmt.Sprintf("The lifecycle nested block %q is defined only for managed resources (\"resource\" blocks), and is not valid for ephemeral resources.", block.Type),
+						Subject:  block.TypeRange.Ptr(),
+					})
 				default:
 					// The cases above should be exhaustive for all block types
 					// defined in the lifecycle schema, so this shouldn't happen.
@@ -685,6 +692,13 @@ func decodeDataBlock(block *hcl.Block, override, nested bool) (*Resource, hcl.Di
 					case "postcondition":
 						r.Postconditions = append(r.Postconditions, cr)
 					}
+				case "action_trigger":
+					diags = append(diags, &hcl.Diagnostic{
+						Severity: hcl.DiagError,
+						Summary:  "Invalid data resource lifecycle nested block",
+						Detail:   fmt.Sprintf("The lifecycle nested block %q is defined only for managed resources (\"resource\" blocks), and is not valid for data resources.", block.Type),
+						Subject:  block.TypeRange.Ptr(),
+					})
 				default:
 					// The cases above should be exhaustive for all block types
 					// defined in the lifecycle schema, so this shouldn't happen.
diff --git a/internal/configs/testdata/invalid-files/data-invalid-action-trigger.tf b/internal/configs/testdata/invalid-files/data-invalid-action-trigger.tf
new file mode 100644
index 0000000000..f4a623f674
--- /dev/null
+++ b/internal/configs/testdata/invalid-files/data-invalid-action-trigger.tf
@@ -0,0 +1,10 @@
+action "test_action" "test" {}
+
+data "test_data" "test" {
+  lifecycle {
+    action_trigger {
+      actions = [action.test_action.test]
+      events  = [after_create, after_update]
+    }
+  }
+}
diff --git a/internal/configs/testdata/invalid-files/ephemeral-invalid-action_trigger.tf b/internal/configs/testdata/invalid-files/ephemeral-invalid-action_trigger.tf
new file mode 100644
index 0000000000..0df5384978
--- /dev/null
+++ b/internal/configs/testdata/invalid-files/ephemeral-invalid-action_trigger.tf
@@ -0,0 +1,10 @@
+action "test_action" "test" {}
+
+ephemeral "test_ephemeral" "test" {
+  lifecycle {
+    action_trigger {
+      actions = [action.test_action.test]
+      events  = [after_create, after_update]
+    }
+  }
+}