diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7139e7ca4d..609f815d8d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ### Fixed
 - Fix false positive in rule spacing-between-declarations-with-annotations ([#1281](https://github.com/pinterest/ktlint/issues/1281))
 - Fix NoSuchElementException for property accessor (`trailing-comma`) ([#1280](https://github.com/pinterest/ktlint/issues/1280))
+- Fix ClassCastException using ktlintFormat on class with KDoc (`no-trailing-spaces`) ([#1270](https://github.com/pinterest/ktlint/issues/1270)
 
 ### Changed
 - Update Kotlin version to `1.6.0` release
diff --git a/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/NoTrailingSpacesRule.kt b/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/NoTrailingSpacesRule.kt
index 229c10d402..0ace64c335 100644
--- a/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/NoTrailingSpacesRule.kt
+++ b/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/NoTrailingSpacesRule.kt
@@ -1,11 +1,14 @@
 package com.pinterest.ktlint.ruleset.standard
 
 import com.pinterest.ktlint.core.Rule
+import com.pinterest.ktlint.core.ast.ElementType.WHITE_SPACE
+import com.pinterest.ktlint.core.ast.isPartOfComment
 import com.pinterest.ktlint.core.ast.nextLeaf
+import com.pinterest.ktlint.core.ast.parent
 import org.jetbrains.kotlin.com.intellij.lang.ASTNode
-import org.jetbrains.kotlin.com.intellij.psi.PsiComment
 import org.jetbrains.kotlin.com.intellij.psi.PsiWhiteSpace
 import org.jetbrains.kotlin.com.intellij.psi.impl.source.tree.LeafPsiElement
+import org.jetbrains.kotlin.kdoc.psi.api.KDoc
 
 class NoTrailingSpacesRule : Rule("no-trailing-spaces") {
 
@@ -14,7 +17,14 @@ class NoTrailingSpacesRule : Rule("no-trailing-spaces") {
         autoCorrect: Boolean,
         emit: (offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit
     ) {
-        if (node is PsiWhiteSpace || node is PsiComment) {
+        if (node.isPartOfKDoc()) {
+            if (node.elementType == WHITE_SPACE && node.hasTrailingSpacesBeforeNewline()) {
+                emit(node.startOffset, "Trailing space(s)", true)
+                if (autoCorrect) {
+                    node.removeTrailingSpacesBeforeNewline()
+                }
+            }
+        } else if (node.elementType == WHITE_SPACE || node.isPartOfComment()) {
             val lines = node.text.split("\n")
             var violated = false
             var violationOffset = node.startOffset
@@ -22,7 +32,8 @@ class NoTrailingSpacesRule : Rule("no-trailing-spaces") {
                 .head()
                 .forEach { line ->
                     if (line.hasTrailingSpace()) {
-                        emit(violationOffset, "Trailing space(s)", true)
+                        val firstTrailingSpaceOffset = violationOffset + line.trimEnd().length
+                        emit(firstTrailingSpaceOffset, "Trailing space(s)", true)
                         violated = true
                     }
                     violationOffset += line.length + 1
@@ -32,7 +43,8 @@ class NoTrailingSpacesRule : Rule("no-trailing-spaces") {
                     // Ignore the last line as it contains the indentation of the next element
                     Unit
                 lines.last().hasTrailingSpace() -> {
-                    emit(violationOffset, "Trailing space(s)", true)
+                    val firstTrailingSpaceOffset = violationOffset + lines.last().trimEnd().length
+                    emit(firstTrailingSpaceOffset, "Trailing space(s)", true)
                     violated = true
                 }
             }
@@ -43,6 +55,21 @@ class NoTrailingSpacesRule : Rule("no-trailing-spaces") {
         }
     }
 
+    private fun ASTNode.isPartOfKDoc() = parent({ it.psi is KDoc }, strict = false) != null
+
+    private fun ASTNode.hasTrailingSpacesBeforeNewline() =
+        text.contains(
+            regex = Regex("\\s+\\n")
+        )
+
+    private fun ASTNode.removeTrailingSpacesBeforeNewline() {
+        val newText = text.replace(
+            regex = Regex("\\s+\\n"),
+            replacement = "\n"
+        )
+        (this as LeafPsiElement).replaceWithText(newText)
+    }
+
     private fun String.hasTrailingSpace() =
         takeLast(1) == " "
 }
diff --git a/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/NoTrailingSpacesRuleTest.kt b/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/NoTrailingSpacesRuleTest.kt
index 07d8837a53..b30573776d 100644
--- a/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/NoTrailingSpacesRuleTest.kt
+++ b/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/NoTrailingSpacesRuleTest.kt
@@ -26,23 +26,41 @@ class NoTrailingSpacesRuleTest {
     }
 
     @Test
-    fun `lint trailing spaces inside block comments`() {
+    fun `trailing spaces inside line comments`() {
         val code =
             """
-            /*${" "}
-             * Some comment${" "}
-             */
+            //${" "}
+            // Some comment${" "}
+            class Foo {
+                //${" "}${" "}
+                // Some comment${" "}${" "}
+                fun bar() = "foobar"
+            }
+            """.trimIndent()
+        val expectedCode =
+            """
+            //
+            // Some comment
+            class Foo {
+                //
+                // Some comment
+                fun bar() = "foobar"
+            }
             """.trimIndent()
 
-        val actual = NoTrailingSpacesRule().lint(code)
-
-        assertThat(actual)
-            .isEqualTo(
-                listOf(
-                    LintError(1, 1, "no-trailing-spaces", "Trailing space(s)"),
-                    LintError(2, 1, "no-trailing-spaces", "Trailing space(s)")
-                )
+        assertThat(
+            NoTrailingSpacesRule().format(code)
+        ).isEqualTo(expectedCode)
+        assertThat(
+            NoTrailingSpacesRule().lint(code)
+        ).isEqualTo(
+            listOf(
+                LintError(1, 3, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(2, 16, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(4, 7, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(5, 20, "no-trailing-spaces", "Trailing space(s)")
             )
+        )
     }
 
     @Test
@@ -52,17 +70,86 @@ class NoTrailingSpacesRuleTest {
             /*${" "}
              * Some comment${" "}
              */
+            class Foo {
+                /*${" "}${" "}
+                 * Some comment${" "}${" "}
+                 */
+                fun bar() = "foobar"
+            }
+            """.trimIndent()
+        val expectedCode =
+            """
+            /*
+             * Some comment
+             */
+            class Foo {
+                /*
+                 * Some comment
+                 */
+                fun bar() = "foobar"
+            }
             """.trimIndent()
 
-        val actual = NoTrailingSpacesRule().format(code)
+        assertThat(
+            NoTrailingSpacesRule().format(code)
+        ).isEqualTo(expectedCode)
+        assertThat(
+            NoTrailingSpacesRule().lint(code)
+        ).isEqualTo(
+            listOf(
+                LintError(1, 3, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(2, 16, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(5, 7, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(6, 20, "no-trailing-spaces", "Trailing space(s)")
+            )
+        )
+    }
 
-        assertThat(actual)
-            .isEqualTo(
-                """
-                /*
+    @Test
+    fun `trailing spaces inside KDoc`() {
+        val code =
+            """
+            /**${" "}
+             * Some comment${" "}
+             *${" "}
+             */
+            class Foo {
+                /**${" "}${" "}
+                 * Some comment${" "}${" "}
+                 *${" "}${" "}
+                 */
+                fun bar() = "foobar"
+            }
+            """.trimIndent()
+        val codeExpected =
+            """
+            /**
+             * Some comment
+             *
+             */
+            class Foo {
+                /**
                  * Some comment
+                 *
                  */
-                """.trimIndent()
+                fun bar() = "foobar"
+            }
+            """.trimIndent()
+
+        assertThat(
+            NoTrailingSpacesRule().format(code)
+        ).isEqualTo(codeExpected)
+        assertThat(
+            NoTrailingSpacesRule().lint(code)
+        ).isEqualTo(
+            listOf(
+                LintError(1, 4, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(2, 16, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(3, 3, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(6, 8, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(7, 20, "no-trailing-spaces", "Trailing space(s)"),
+                LintError(8, 7, "no-trailing-spaces", "Trailing space(s)"),
             )
+        )
     }
 }