diff --git a/packages/core/src/features/st-mixin.ts b/packages/core/src/features/st-mixin.ts
index 00dbc8208..e7d1ac357 100644
--- a/packages/core/src/features/st-mixin.ts
+++ b/packages/core/src/features/st-mixin.ts
@@ -183,7 +183,7 @@ export class StylablePublicApi {
                     name,
                     kind: 'js-func',
                     args: [],
-                    func: resolvedSymbols.js[name].symbol,
+                    func: resolvedSymbols.js[name].symbol as (...args: any[]) => any,
                 };
                 for (const arg of Object.values(data.options)) {
                     mixRef.args.push(arg.value);
@@ -374,10 +374,10 @@ function appendMixin(context: FeatureTransformContext, config: ApplyMixinContext
         handleCSSMixin(context, config, resolveChain);
         return;
     } else if (resolvedType === `js`) {
-        const resolvedMixin = resolvedSymbols.js[symbolName];
-        if (typeof resolvedMixin.symbol === 'function') {
+        const jsValue = resolvedSymbols.js[symbolName].symbol;
+        if (typeof jsValue === 'function') {
             try {
-                handleJSMixin(context, config, resolvedMixin.symbol);
+                handleJSMixin(context, config, jsValue as (...args: any[]) => any);
             } catch (e) {
                 context.diagnostics.report(diagnostics.FAILED_TO_APPLY_MIXIN(String(e)), {
                     node: config.rule,
diff --git a/packages/core/src/features/st-var.ts b/packages/core/src/features/st-var.ts
index dc75f5d7f..ae870ff84 100644
--- a/packages/core/src/features/st-var.ts
+++ b/packages/core/src/features/st-var.ts
@@ -400,21 +400,16 @@ function evaluateValueCall(
             const type = resolvedSymbols.mainNamespace[varName];
             if (type === `js`) {
                 const deepResolve = resolvedSymbols.js[varName];
-                const importedType = typeof deepResolve.symbol;
-                if (importedType === 'string') {
+                const jsValue = deepResolve.symbol;
+                if (typeof jsValue === 'string') {
                     parsedNode.resolvedValue = context.evaluator.valueHook
-                        ? context.evaluator.valueHook(
-                              deepResolve.symbol,
-                              varName,
-                              false,
-                              passedThrough
-                          )
-                        : deepResolve.symbol;
+                        ? context.evaluator.valueHook(jsValue, varName, false, passedThrough)
+                        : jsValue;
                 } else if (node) {
                     // unsupported Javascript value
                     // ToDo: provide actual exported id (default/named as x)
                     context.diagnostics.report(
-                        diagnostics.CANNOT_USE_JS_AS_VALUE(importedType, varName),
+                        diagnostics.CANNOT_USE_JS_AS_VALUE(typeof jsValue, varName),
                         {
                             node,
                             word: varName,
@@ -480,7 +475,7 @@ export function resolveReferencedVarNames(
                     break;
                 case 'import': {
                     const resolved = context.resolver.deepResolve(symbol);
-                    if (resolved?._kind === 'css' && resolved.symbol._kind === 'var') {
+                    if (resolved?._kind === 'css' && resolved.symbol?._kind === 'var') {
                         varsToCheck.push({ meta: resolved.meta, name: resolved.symbol.name });
                     }
                     break;
diff --git a/packages/core/src/functions.ts b/packages/core/src/functions.ts
index 9bf44bc38..13a4ccda2 100644
--- a/packages/core/src/functions.ts
+++ b/packages/core/src/functions.ts
@@ -186,7 +186,10 @@ export function processDeclarationValue(
                 const formatter = resolvedSymbols.js[value];
                 const formatterArgs = getFormatterArgs(parsedNode);
                 try {
-                    parsedNode.resolvedValue = formatter.symbol.apply(null, formatterArgs);
+                    // ToDo: check if function instead of calling on a non function
+                    parsedNode.resolvedValue = (formatter.symbol as (...args: any[]) => any)(
+                        ...formatterArgs
+                    );
                     if (evaluator.valueHook && typeof parsedNode.resolvedValue === 'string') {
                         parsedNode.resolvedValue = evaluator.valueHook(
                             parsedNode.resolvedValue,
diff --git a/packages/core/src/index-internal.ts b/packages/core/src/index-internal.ts
index b8361725e..c76956052 100644
--- a/packages/core/src/index-internal.ts
+++ b/packages/core/src/index-internal.ts
@@ -47,7 +47,12 @@ export {
     EmitDiagnosticsContext,
     reportDiagnostic,
 } from './report-diagnostic';
-export { StylableResolver, StylableResolverCache } from './stylable-resolver';
+export {
+    StylableResolver,
+    StylableResolverCache,
+    isValidCSSResolve,
+    CSSResolveMaybe,
+} from './stylable-resolver';
 export { CacheItem, FileProcessor, cachedProcessFile, processFn } from './cached-process-file';
 export { createStylableFileProcessor } from './create-stylable-processor';
 export { packageNamespaceFactory } from './resolve-namespace-factories';
diff --git a/packages/core/src/stylable-resolver.ts b/packages/core/src/stylable-resolver.ts
index c84da2c9e..40605c813 100644
--- a/packages/core/src/stylable-resolver.ts
+++ b/packages/core/src/stylable-resolver.ts
@@ -63,16 +63,26 @@ export type CachedModuleEntity =
 
 export type StylableResolverCache = Map<string, CachedModuleEntity>;
 
+export interface CSSResolveMaybe<
+    T extends StylableSymbol | STStructure.PartSymbol = StylableSymbol
+> {
+    _kind: 'css';
+    symbol: T | undefined;
+    meta: StylableMeta;
+}
 export interface CSSResolve<T extends StylableSymbol | STStructure.PartSymbol = StylableSymbol> {
     _kind: 'css';
     symbol: T;
     meta: StylableMeta;
 }
+export function isValidCSSResolve(resolved: CSSResolveMaybe): resolved is CSSResolve {
+    return resolved.symbol !== undefined;
+}
 export type CSSResolvePath = Array<CSSResolve<ClassSymbol | ElementSymbol>>;
 
 export interface JSResolve {
     _kind: 'js';
-    symbol: any;
+    symbol: unknown;
     meta: null;
 }
 
@@ -91,7 +101,7 @@ export interface MetaResolvedSymbols {
 }
 
 export type ReportError = (
-    res: CSSResolve | JSResolve | null,
+    res: CSSResolveMaybe | JSResolve | null,
     extend: ImportSymbol | ClassSymbol | ElementSymbol,
     extendPath: Array<CSSResolve<ClassSymbol | ElementSymbol>>,
     meta: StylableMeta,
@@ -192,7 +202,7 @@ export class StylableResolver {
         imported: Imported,
         name: string,
         subtype: 'mappedSymbols' | 'mappedKeyframes' | STSymbol.Namespaces = 'mappedSymbols'
-    ): CSSResolve | JSResolve | null {
+    ): CSSResolveMaybe | JSResolve | null {
         const res = this.getModule(imported);
         if (res.value === null) {
             return null;
@@ -226,7 +236,7 @@ export class StylableResolver {
         const name = importSymbol.type === 'named' ? importSymbol.name : '';
         return this.resolveImported(importSymbol.import, name);
     }
-    public resolve(maybeImport: StylableSymbol | undefined): CSSResolve | JSResolve | null {
+    public resolve(maybeImport: StylableSymbol | undefined): CSSResolveMaybe | JSResolve | null {
         if (!maybeImport || maybeImport._kind !== 'import') {
             if (
                 maybeImport &&
@@ -261,7 +271,7 @@ export class StylableResolver {
     public deepResolve(
         maybeImport: StylableSymbol | undefined,
         path: StylableSymbol[] = []
-    ): CSSResolve | JSResolve | null {
+    ): CSSResolveMaybe | JSResolve | null {
         let resolved = this.resolve(maybeImport);
         while (
             resolved &&
@@ -334,7 +344,7 @@ export class StylableResolver {
         };
         // resolve main namespace
         for (const [name, symbol] of Object.entries(meta.getAllSymbols())) {
-            let deepResolved: CSSResolve | JSResolve | null;
+            let deepResolved: CSSResolveMaybe | JSResolve | null;
             if (symbol._kind === `import` || (symbol._kind === `cssVar` && symbol.alias)) {
                 deepResolved = this.deepResolve(symbol);
                 if (!deepResolved || !deepResolved.symbol) {
@@ -366,13 +376,19 @@ export class StylableResolver {
             } else {
                 deepResolved = { _kind: `css`, meta, symbol };
             }
-            switch (deepResolved.symbol._kind) {
+            // deepResolved symbol is resolved by this point
+            switch (deepResolved.symbol!._kind) {
                 case `class`:
                     resolvedSymbols.class[name] = this.resolveExtends(
                         meta,
-                        deepResolved.symbol,
+                        deepResolved.symbol!,
                         false,
-                        validateClassResolveExtends(meta, name, diagnostics, deepResolved)
+                        validateClassResolveExtends(
+                            meta,
+                            name,
+                            diagnostics,
+                            deepResolved as CSSResolve<ClassSymbol>
+                        )
                     );
                     break;
                 case `element`:
@@ -385,7 +401,7 @@ export class StylableResolver {
                     resolvedSymbols.cssVar[name] = deepResolved as CSSResolve<CSSVarSymbol>;
                     break;
             }
-            resolvedSymbols.mainNamespace[name] = deepResolved.symbol._kind;
+            resolvedSymbols.mainNamespace[name] = deepResolved.symbol!._kind;
         }
         // resolve keyframes
         for (const [name, symbol] of Object.entries(CSSKeyframes.getAll(meta))) {
@@ -497,7 +513,7 @@ function validateClassResolveExtends(
     meta: StylableMeta,
     name: string,
     diagnostics: Diagnostics,
-    deepResolved: CSSResolve<StylableSymbol> | JSResolve | null
+    deepResolved: CSSResolve<ClassSymbol>
 ): ReportError | undefined {
     return (res, extend) => {
         const decl = findRule(meta.sourceAst, '.' + name);
@@ -520,7 +536,7 @@ function validateClassResolveExtends(
                 });
             }
         } else {
-            if (deepResolved?.symbol.alias) {
+            if (deepResolved.symbol.alias) {
                 meta.sourceAst.walkRules(new RegExp('\\.' + name), (rule) => {
                     diagnostics.report(CSSClass.diagnostics.UNKNOWN_IMPORT_ALIAS(name), {
                         node: rule,
diff --git a/packages/language-service/src/lib/completion-providers.ts b/packages/language-service/src/lib/completion-providers.ts
index fc18c8c0c..94a7dbfee 100644
--- a/packages/language-service/src/lib/completion-providers.ts
+++ b/packages/language-service/src/lib/completion-providers.ts
@@ -565,6 +565,7 @@ export const ExtendCompletionPlugin: LangServicePlugin = {
                             return (
                                 res &&
                                 res._kind === 'css' &&
+                                res.symbol &&
                                 (res.symbol._kind === 'class' || res.symbol._kind === 'element')
                             );
                         })
diff --git a/packages/language-service/src/lib/provider.ts b/packages/language-service/src/lib/provider.ts
index f9ae236d8..96225a42e 100644
--- a/packages/language-service/src/lib/provider.ts
+++ b/packages/language-service/src/lib/provider.ts
@@ -10,7 +10,6 @@ import {
     ImportSymbol,
     Stylable,
     StylableMeta,
-    JSResolve,
     Diagnostics,
 } from '@stylable/core';
 import {
@@ -18,6 +17,8 @@ import {
     StylableProcessor,
     STCustomSelector,
     MappedStates,
+    type StylableResolver,
+    isValidCSSResolve,
 } from '@stylable/core/dist/index-internal';
 import type {
     Location,
@@ -202,7 +203,7 @@ export class Provider {
                     break;
                 }
                 case 'import': {
-                    let resolved: CSSResolve | JSResolve | null = null;
+                    let resolved: ReturnType<StylableResolver['resolve']> = null;
                     try {
                         resolved = this.stylable.resolver.resolve(symbol);
                     } catch {
@@ -321,29 +322,24 @@ export class Provider {
         state: string
     ): CSSResolve | null {
         const importedSymbol = origMeta.getClass(elementName)![`-st-extends`];
-        let res: CSSResolve | JSResolve | null = null;
+        let res: ReturnType<StylableResolver['resolveImport']> = null;
 
         if (importedSymbol && importedSymbol._kind === 'import') {
             res = this.stylable.resolver.resolveImport(importedSymbol);
         }
 
         const localSymbol = origMeta.getSymbol(elementName)!;
-        if (
-            res &&
-            res._kind === 'css' &&
-            Object.keys((res.symbol as ClassSymbol)[`-st-states`]!).includes(state)
-        ) {
-            return res;
-        } else if (
-            res &&
-            res._kind === 'css' &&
-            (localSymbol._kind === 'class' || localSymbol._kind === 'element') &&
-            localSymbol[`-st-extends`]
-        ) {
-            return this.findMyState(res.meta, res.symbol.name, state);
-        } else {
-            return null;
+        if (res && res._kind === 'css' && isValidCSSResolve(res)) {
+            if (Object.keys((res.symbol as ClassSymbol)[`-st-states`]!).includes(state)) {
+                return res;
+            } else if (
+                (localSymbol._kind === 'class' || localSymbol._kind === 'element') &&
+                localSymbol[`-st-extends`]
+            ) {
+                return this.findMyState(res.meta, res.symbol.name, state);
+            }
         }
+        return null;
     }
 
     public getSignatureHelp(
diff --git a/packages/webpack-extensions/src/types.ts b/packages/webpack-extensions/src/types.ts
index 2742092e5..b9167ca7d 100644
--- a/packages/webpack-extensions/src/types.ts
+++ b/packages/webpack-extensions/src/types.ts
@@ -1,4 +1,5 @@
-import type { CSSResolve, Imported, JSResolve, StylableMeta } from '@stylable/core';
+import type { Imported, JSResolve, StylableMeta } from '@stylable/core';
+import type { CSSResolveMaybe } from '@stylable/core/dist/index-internal';
 
 export interface Metadata {
     entry: string;
@@ -24,5 +25,5 @@ export type MetadataList = Array<{
 
 export type ResolvedImport = {
     stImport: Imported;
-    resolved: CSSResolve | JSResolve | null;
+    resolved: CSSResolveMaybe | JSResolve | null;
 };