diff --git a/src/main/kotlin/org/pkl/lsp/analyzers/MemberAnalyzer.kt b/src/main/kotlin/org/pkl/lsp/analyzers/MemberAnalyzer.kt
index f21e867a..fcdef0eb 100644
--- a/src/main/kotlin/org/pkl/lsp/analyzers/MemberAnalyzer.kt
+++ b/src/main/kotlin/org/pkl/lsp/analyzers/MemberAnalyzer.kt
@@ -19,10 +19,16 @@ import org.eclipse.lsp4j.DiagnosticSeverity
 import org.pkl.lsp.ErrorMessages
 import org.pkl.lsp.PklBaseModule
 import org.pkl.lsp.Project
+import org.pkl.lsp.ast.PklClassMember
+import org.pkl.lsp.ast.PklClassMethod
 import org.pkl.lsp.ast.PklClassProperty
+import org.pkl.lsp.ast.PklExpr
 import org.pkl.lsp.ast.PklNode
 import org.pkl.lsp.ast.PklObjectProperty
 import org.pkl.lsp.ast.PklProperty
+import org.pkl.lsp.ast.Span
+import org.pkl.lsp.ast.Terminal
+import org.pkl.lsp.ast.TokenType
 import org.pkl.lsp.packages.dto.PklProject
 import org.pkl.lsp.resolvers.ResolveVisitors
 import org.pkl.lsp.resolvers.Resolvers
@@ -56,6 +62,10 @@ class MemberAnalyzer(project: Project) : Analyzer(project) {
       }
       is PklClassProperty -> {
         checkUnresolvedProperty(node, memberType, base, diagnosticsHolder, context)
+        checkAbstractMemberWithBody(node, diagnosticsHolder)
+      }
+      is PklClassMethod -> {
+        checkAbstractMemberWithBody(node, diagnosticsHolder)
       }
     }
     return true
@@ -100,4 +110,33 @@ class MemberAnalyzer(project: Project) : Analyzer(project) {
       }
     }
   }
+
+  private fun checkAbstractMemberWithBody(
+    node: PklClassMember,
+    diagnosticsHolder: DiagnosticsHolder,
+  ) {
+    if (!node.isAbstract) return
+    val bodySpan =
+      if (node is PklClassProperty) {
+        node.expr?.spanWithAssign ?: node.objectBody?.span
+      } else {
+        node as PklClassMethod
+        node.body?.spanWithAssign
+      }
+    if (bodySpan != null) {
+      diagnosticsHolder.addDiagnostic(
+        node,
+        "Abstract member cannot have a body",
+        bodySpan,
+        DiagnosticSeverity.Error,
+      )
+    }
+  }
+
+  private val PklExpr.spanWithAssign: Span?
+    get() {
+      val assignNode =
+        this.prevSiblingMatching { it is Terminal && it.type == TokenType.ASSIGN } ?: return null
+      return assignNode.span.endAt(span)
+    }
 }
diff --git a/src/main/kotlin/org/pkl/lsp/ast/PklNode.kt b/src/main/kotlin/org/pkl/lsp/ast/PklNode.kt
index f7167924..9ac7ea06 100644
--- a/src/main/kotlin/org/pkl/lsp/ast/PklNode.kt
+++ b/src/main/kotlin/org/pkl/lsp/ast/PklNode.kt
@@ -82,6 +82,14 @@ interface PklNode {
     val parentNode = parent ?: return null
     return parentNode.children[index - 1]
   }
+
+  fun prevSiblingMatching(filter: (PklNode) -> Boolean): PklNode? {
+    var node = prevSibling()
+    while (node != null && !filter(node)) {
+      node = node.prevSibling()
+    }
+    return node
+  }
 }
 
 sealed interface PklSuppressWarningsTarget : PklNode {
diff --git a/src/test/files/DiagnosticsSnippetTests/inputs/member/abstractMemberWithBody.pkl b/src/test/files/DiagnosticsSnippetTests/inputs/member/abstractMemberWithBody.pkl
new file mode 100644
index 00000000..1e3b8e95
--- /dev/null
+++ b/src/test/files/DiagnosticsSnippetTests/inputs/member/abstractMemberWithBody.pkl
@@ -0,0 +1,7 @@
+abstract module MyMod
+
+abstract foo = 1
+
+abstract bar {}
+
+abstract function foo() = 1
diff --git a/src/test/files/DiagnosticsSnippetTests/outputs/member/abstractMemberWithBody.txt b/src/test/files/DiagnosticsSnippetTests/outputs/member/abstractMemberWithBody.txt
new file mode 100644
index 00000000..ee538c17
--- /dev/null
+++ b/src/test/files/DiagnosticsSnippetTests/outputs/member/abstractMemberWithBody.txt
@@ -0,0 +1,14 @@
+ abstract module MyMod
+ 
+ abstract foo = 1
+              ^^^
+| Error: Abstract member cannot have a body
+ 
+ abstract bar {}
+              ^^
+| Error: Abstract member cannot have a body
+ 
+ abstract function foo() = 1
+                         ^^^
+| Error: Abstract member cannot have a body
+ 
\ No newline at end of file
diff --git a/src/test/kotlin/org/pkl/lsp/ModifierQuickfixTest.kt b/src/test/kotlin/org/pkl/lsp/ModifierQuickfixTest.kt
index b3b76f8d..44115824 100644
--- a/src/test/kotlin/org/pkl/lsp/ModifierQuickfixTest.kt
+++ b/src/test/kotlin/org/pkl/lsp/ModifierQuickfixTest.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright © 2025 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2025-2026 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -53,7 +53,7 @@ class ModifierQuickfixTest : LspTestBase() {
         """
      amends "pkl:test"
 
-     abstract external foo: String = "Hello"
+     const foo: String = "Hello"
     """
           .trimIndent()
       )
@@ -62,13 +62,12 @@ class ModifierQuickfixTest : LspTestBase() {
     val action = diagnostic.actions.find { it.title == "Add modifier 'local'" }
     assertThat(action).isNotNull
     runAction(action!!.toMessage(diagnostic))
-    // modifier gets inserted in between 'abstract' and 'external'
     assertThat(file.contents)
       .isEqualTo(
         """
      amends "pkl:test"
 
-     abstract local external foo: String = "Hello"
+     local const foo: String = "Hello"
     """
           .trimIndent()
       )