diff --git a/Sources/SwiftParser/Declarations.swift b/Sources/SwiftParser/Declarations.swift
index 6cd0a74cb34..87f12d1907e 100644
--- a/Sources/SwiftParser/Declarations.swift
+++ b/Sources/SwiftParser/Declarations.swift
@@ -17,11 +17,11 @@ extension DeclarationModifier {
     switch self {
     case .__consuming, .__setter_access, ._const, ._local, .async,
       .borrowing, .class, .consuming, .convenience, .distributed, .dynamic,
-      .final, .indirect, .infix, .isolated, .lazy, .mutating, .nonisolated,
-      .nonmutating, .optional, .override, .postfix, .prefix, .reasync,
-      .required, .rethrows, .static, .weak:
+      .final, .indirect, .infix, .isolated, .lazy, .mutating, .nonmutating,
+      .optional, .override, .postfix, .prefix, .reasync, .required,
+      .rethrows, .static, .weak:
       return false
-    case .fileprivate, .internal, .package, .open, .private,
+    case .fileprivate, .internal, .nonisolated, .package, .open, .private,
       .public, .unowned:
       return true
     }
diff --git a/Sources/SwiftParser/Modifiers.swift b/Sources/SwiftParser/Modifiers.swift
index a28e44c2343..39588f47b95 100644
--- a/Sources/SwiftParser/Modifiers.swift
+++ b/Sources/SwiftParser/Modifiers.swift
@@ -60,6 +60,8 @@ extension Parser {
         }
       case (.declarationModifier(.unowned), let handle)?:
         elements.append(self.parseUnownedModifier(handle))
+      case (.declarationModifier(.nonisolated), let handle)?:
+        elements.append(parseNonisolatedModifier(handle))
       case (.declarationModifier(.final), let handle)?,
         (.declarationModifier(.required), let handle)?,
         (.declarationModifier(.optional), let handle)?,
@@ -79,7 +81,6 @@ extension Parser {
         (.declarationModifier(.indirect), let handle)?,
         (.declarationModifier(.isolated), let handle)?,
         (.declarationModifier(.async), let handle)?,
-        (.declarationModifier(.nonisolated), let handle)?,
         (.declarationModifier(.distributed), let handle)?,
         (.declarationModifier(._const), let handle)?,
         (.declarationModifier(._local), let handle)?,
@@ -98,9 +99,9 @@ extension Parser {
 }
 
 extension Parser {
-  mutating func parseModifierDetail() -> RawDeclModifierDetailSyntax {
+  mutating func parseModifierDetail(_ keyword: Keyword) -> RawDeclModifierDetailSyntax {
     let (unexpectedBeforeLeftParen, leftParen) = self.expect(.leftParen)
-    let (unexpectedBeforeDetailToken, detailToken) = self.expect(.identifier, TokenSpec(.set, remapping: .identifier), default: .identifier)
+    let (unexpectedBeforeDetailToken, detailToken) = self.expect(.identifier, TokenSpec(keyword, remapping: .identifier), default: .identifier)
     let (unexpectedBeforeRightParen, rightParen) = self.expect(.rightParen)
     return RawDeclModifierDetailSyntax(
       unexpectedBeforeLeftParen,
@@ -118,7 +119,7 @@ extension Parser {
 
     let detail: RawDeclModifierDetailSyntax?
     if self.at(.leftParen) {
-      detail = self.parseModifierDetail()
+      detail = self.parseModifierDetail(.set)
     } else {
       detail = nil
     }
@@ -217,4 +218,22 @@ extension Parser {
       arena: self.arena
     )
   }
+
+  mutating func parseNonisolatedModifier(_ handle: RecoveryConsumptionHandle) -> RawDeclModifierSyntax {
+    let (unexpectedBeforeKeyword, keyword) = self.eat(handle)
+
+    let detail: RawDeclModifierDetailSyntax?
+    if self.at(.leftParen) {
+      detail = self.parseModifierDetail(.unsafe)
+    } else {
+      detail = nil
+    }
+
+    return RawDeclModifierSyntax(
+      unexpectedBeforeKeyword,
+      name: keyword,
+      detail: detail,
+      arena: self.arena
+    )
+  }
 }
diff --git a/Tests/SwiftParserTest/DeclarationTests.swift b/Tests/SwiftParserTest/DeclarationTests.swift
index ee24ab0d121..511b980c50a 100644
--- a/Tests/SwiftParserTest/DeclarationTests.swift
+++ b/Tests/SwiftParserTest/DeclarationTests.swift
@@ -240,6 +240,19 @@ final class DeclarationTests: ParserTestCase {
     )
   }
 
+  func testNonisolatedUnsafeParsing() {
+    assertParse(
+      """
+      nonisolated(unsafe) let a = 0
+
+      struct A {
+        nonisolated(unsafe) let b = 0
+        nonisolated(unsafe) var c: Int { 0 }
+      }
+      """
+    )
+  }
+
   func testProtocolParsing() {
     assertParse("protocol Foo {}")