diff --git a/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java b/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java
index f70f14f3ff2..3e2fb2e5769 100644
--- a/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java
+++ b/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java
@@ -19270,6 +19270,12 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
             runTest("compiler/testData/codegen/box/inlineClasses/passInlineClassWithSpreadOperatorToVarargs.kt");
         }
 
+        @Test
+        @TestMetadata("privateConstructorFunInterfaceMultiModule.kt")
+        public void testPrivateConstructorFunInterfaceMultiModule() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/privateConstructorFunInterfaceMultiModule.kt");
+        }
+
         @Test
         @TestMetadata("propertyLoweringOrder.kt")
         public void testPropertyLoweringOrder() throws Exception {
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/indy/LambdaMetafactoryArguments.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/indy/LambdaMetafactoryArguments.kt
index 3749ad1e401..39173ca61da 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/indy/LambdaMetafactoryArguments.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/indy/LambdaMetafactoryArguments.kt
@@ -481,8 +481,7 @@ internal class LambdaMetafactoryArgumentsBuilder(
         if (erasedAdapteeClass.isInline) {
             // Inline classes mapped to non-null reference types are a special case because they can't be boxed trivially.
             // TODO consider adding a special type annotation to force boxing on an inline class type regardless of its underlying type.
-            val underlyingAdapteeType = getInlineClassUnderlyingType(erasedAdapteeClass) as? IrSimpleType
-                ?: throw AssertionError("Underlying type for inline class should be a simple type: ${erasedAdapteeClass.render()}")
+            val underlyingAdapteeType = getInlineClassUnderlyingType(erasedAdapteeClass)
             if (!underlyingAdapteeType.hasQuestionMark && !underlyingAdapteeType.isPrimitiveType()) {
                 return TypeAdaptationConstraint.CONFLICT
             }
diff --git a/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/TypeTransformer.kt b/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/TypeTransformer.kt
index 6aab0dddbf2..f130ff41d1c 100644
--- a/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/TypeTransformer.kt
+++ b/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/TypeTransformer.kt
@@ -14,7 +14,6 @@ import org.jetbrains.kotlin.ir.symbols.IrTypeParameterSymbol
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.classifierOrNull
 import org.jetbrains.kotlin.ir.types.getClass
-import org.jetbrains.kotlin.ir.util.getInlineClassUnderlyingType
 import org.jetbrains.kotlin.ir.util.isInterface
 import org.jetbrains.kotlin.wasm.ir.*
 
@@ -97,7 +96,7 @@ class WasmTypeTransformer(
                 if (klass != null && klass.hasWasmForeignAnnotation()) {
                     WasmExternRef
                 } else if (ic != null) {
-                    getInlineClassUnderlyingType(ic).toWasmValueType()
+                    context.backendContext.inlineClassesUtils.getInlineClassUnderlyingType(ic).toWasmValueType()
                 } else {
                     this.toWasmGcRefType()
                 }
diff --git a/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/utils/WasmInlineClassesUtils.kt b/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/utils/WasmInlineClassesUtils.kt
index 714bc9e45b0..8bbef3d48c1 100644
--- a/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/utils/WasmInlineClassesUtils.kt
+++ b/compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/utils/WasmInlineClassesUtils.kt
@@ -9,10 +9,12 @@ import org.jetbrains.kotlin.backend.wasm.WasmSymbols
 import org.jetbrains.kotlin.ir.backend.js.InlineClassesUtils
 import org.jetbrains.kotlin.ir.backend.js.utils.erase
 import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrConstructor
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
 import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.isNullable
+import org.jetbrains.kotlin.ir.util.fqNameWhenAvailable
 
 class WasmInlineClassesUtils(private val wasmSymbols: WasmSymbols) : InlineClassesUtils {
     override fun isTypeInlined(type: IrType): Boolean {
@@ -42,4 +44,17 @@ class WasmInlineClassesUtils(private val wasmSymbols: WasmSymbols) : InlineClass
 
     override val unboxIntrinsic: IrSimpleFunctionSymbol
         get() = wasmSymbols.unboxIntrinsic
-}
\ No newline at end of file
+
+    /**
+     * Unlike [org.jetbrains.kotlin.ir.util.getInlineClassUnderlyingType], doesn't use [IrClass.inlineClassRepresentation] because
+     * for some reason it can be called for classes which are not inline, e.g. `kotlin.Double`.
+     */
+    fun getInlineClassUnderlyingType(irClass: IrClass): IrType {
+        for (declaration in irClass.declarations) {
+            if (declaration is IrConstructor && declaration.isPrimary) {
+                return declaration.valueParameters[0].type
+            }
+        }
+        error("Class has no primary constructor: ${irClass.fqNameWhenAvailable}")
+    }
+}
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/InlineClasses.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/InlineClasses.kt
index ecfc42a142d..1435ee5d6b5 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/InlineClasses.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/InlineClasses.kt
@@ -6,18 +6,13 @@
 package org.jetbrains.kotlin.ir.util
 
 import org.jetbrains.kotlin.ir.declarations.IrClass
-import org.jetbrains.kotlin.ir.declarations.IrConstructor
 import org.jetbrains.kotlin.ir.declarations.IrField
 import org.jetbrains.kotlin.ir.declarations.IrProperty
-import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.IrSimpleType
 
-fun getInlineClassUnderlyingType(irClass: IrClass): IrType {
-    for (declaration in irClass.declarations) {
-        if (declaration is IrConstructor && declaration.isPrimary) {
-            return declaration.valueParameters[0].type
-        }
-    }
-    error("Inline class has no primary constructor: ${irClass.fqNameWhenAvailable}")
+fun getInlineClassUnderlyingType(irClass: IrClass): IrSimpleType {
+    val representation = irClass.inlineClassRepresentation ?: error("Not an inline class: ${irClass.render()}")
+    return representation.underlyingType
 }
 
 fun getInlineClassBackingField(irClass: IrClass): IrField {
diff --git a/compiler/testData/codegen/box/inlineClasses/privateConstructorFunInterfaceMultiModule.kt b/compiler/testData/codegen/box/inlineClasses/privateConstructorFunInterfaceMultiModule.kt
new file mode 100644
index 00000000000..2adb206661c
--- /dev/null
+++ b/compiler/testData/codegen/box/inlineClasses/privateConstructorFunInterfaceMultiModule.kt
@@ -0,0 +1,23 @@
+// IGNORE_BACKEND: WASM
+// MODULE: lib
+// FILE: lib.kt
+
+inline class Z private constructor(private val value: Any?) {
+    fun result(): String = value as String
+
+    companion object {
+        fun create(value: Any?): Z = Z(value)
+    }
+}
+
+fun interface IFoo<T> {
+    fun foo(x: T): String
+}
+
+fun foo1(fs: IFoo<Z>) = fs.foo(Z.create("OK"))
+
+// MODULE: main(lib)
+// FILE: main.kt
+
+fun box(): String =
+    foo1 { it.result() }
diff --git a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java
index 847659d0cb3..bfecb7b16c1 100644
--- a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java
+++ b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java
@@ -19114,6 +19114,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             runTest("compiler/testData/codegen/box/inlineClasses/passInlineClassWithSpreadOperatorToVarargs.kt");
         }
 
+        @Test
+        @TestMetadata("privateConstructorFunInterfaceMultiModule.kt")
+        public void testPrivateConstructorFunInterfaceMultiModule() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/privateConstructorFunInterfaceMultiModule.kt");
+        }
+
         @Test
         @TestMetadata("propertyLoweringOrder.kt")
         public void testPropertyLoweringOrder() throws Exception {
diff --git a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java
index 45dc7f7a2dc..c0556b0333a 100644
--- a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java
+++ b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java
@@ -19270,6 +19270,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             runTest("compiler/testData/codegen/box/inlineClasses/passInlineClassWithSpreadOperatorToVarargs.kt");
         }
 
+        @Test
+        @TestMetadata("privateConstructorFunInterfaceMultiModule.kt")
+        public void testPrivateConstructorFunInterfaceMultiModule() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/privateConstructorFunInterfaceMultiModule.kt");
+        }
+
         @Test
         @TestMetadata("propertyLoweringOrder.kt")
         public void testPropertyLoweringOrder() throws Exception {
diff --git a/compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java b/compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java
index a0017f0dd69..d8526b62441 100644
--- a/compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java
+++ b/compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java
@@ -15867,6 +15867,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/inlineClasses/passInlineClassWithSpreadOperatorToVarargs.kt");
         }
 
+        @TestMetadata("privateConstructorFunInterfaceMultiModule.kt")
+        public void testPrivateConstructorFunInterfaceMultiModule() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/privateConstructorFunInterfaceMultiModule.kt");
+        }
+
         @TestMetadata("propertyLoweringOrder.kt")
         public void testPropertyLoweringOrder() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/propertyLoweringOrder.kt");
diff --git a/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/es6/semantics/IrJsCodegenBoxES6TestGenerated.java b/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/es6/semantics/IrJsCodegenBoxES6TestGenerated.java
index 29d595f6e45..d24754a368d 100644
--- a/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/es6/semantics/IrJsCodegenBoxES6TestGenerated.java
+++ b/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/es6/semantics/IrJsCodegenBoxES6TestGenerated.java
@@ -13816,6 +13816,11 @@ public class IrJsCodegenBoxES6TestGenerated extends AbstractIrJsCodegenBoxES6Tes
             runTest("compiler/testData/codegen/box/inlineClasses/passInlineClassWithSpreadOperatorToVarargs.kt");
         }
 
+        @TestMetadata("privateConstructorFunInterfaceMultiModule.kt")
+        public void testPrivateConstructorFunInterfaceMultiModule() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/privateConstructorFunInterfaceMultiModule.kt");
+        }
+
         @TestMetadata("propertyLoweringOrder.kt")
         public void testPropertyLoweringOrder() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/propertyLoweringOrder.kt");
diff --git a/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/ir/semantics/IrJsCodegenBoxTestGenerated.java b/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/ir/semantics/IrJsCodegenBoxTestGenerated.java
index 53664e72bdb..693cbb3a1d7 100644
--- a/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/ir/semantics/IrJsCodegenBoxTestGenerated.java
+++ b/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/ir/semantics/IrJsCodegenBoxTestGenerated.java
@@ -13222,6 +13222,11 @@ public class IrJsCodegenBoxTestGenerated extends AbstractIrJsCodegenBoxTest {
             runTest("compiler/testData/codegen/box/inlineClasses/passInlineClassWithSpreadOperatorToVarargs.kt");
         }
 
+        @TestMetadata("privateConstructorFunInterfaceMultiModule.kt")
+        public void testPrivateConstructorFunInterfaceMultiModule() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/privateConstructorFunInterfaceMultiModule.kt");
+        }
+
         @TestMetadata("propertyLoweringOrder.kt")
         public void testPropertyLoweringOrder() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/propertyLoweringOrder.kt");
diff --git a/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java b/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java
index b963e8722fd..bc4d0767233 100644
--- a/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java
+++ b/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java
@@ -13287,6 +13287,11 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             runTest("compiler/testData/codegen/box/inlineClasses/passInlineClassWithSpreadOperatorToVarargs.kt");
         }
 
+        @TestMetadata("privateConstructorFunInterfaceMultiModule.kt")
+        public void testPrivateConstructorFunInterfaceMultiModule() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/privateConstructorFunInterfaceMultiModule.kt");
+        }
+
         @TestMetadata("propertyLoweringOrder.kt")
         public void testPropertyLoweringOrder() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/propertyLoweringOrder.kt");
diff --git a/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/wasm/semantics/IrCodegenBoxWasmTestGenerated.java b/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/wasm/semantics/IrCodegenBoxWasmTestGenerated.java
index 385b9263adb..37833c62cb8 100644
--- a/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/wasm/semantics/IrCodegenBoxWasmTestGenerated.java
+++ b/js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/wasm/semantics/IrCodegenBoxWasmTestGenerated.java
@@ -7277,6 +7277,11 @@ public class IrCodegenBoxWasmTestGenerated extends AbstractIrCodegenBoxWasmTest
             runTest("compiler/testData/codegen/box/inlineClasses/passInlineClassWithSpreadOperatorToVarargs.kt");
         }
 
+        @TestMetadata("privateConstructorFunInterfaceMultiModule.kt")
+        public void testPrivateConstructorFunInterfaceMultiModule() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/privateConstructorFunInterfaceMultiModule.kt");
+        }
+
         @TestMetadata("propertyLoweringOrder.kt")
         public void testPropertyLoweringOrder() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/propertyLoweringOrder.kt");