diff --git a/actions-languageservice/src/complete.ts b/actions-languageservice/src/complete.ts
index 061561a..da3b550 100644
--- a/actions-languageservice/src/complete.ts
+++ b/actions-languageservice/src/complete.ts
@@ -117,7 +117,7 @@ async function getValues(
     (parent.definition?.key && defaultValueProviders[parent.definition.key]);
 
   if (valueProvider) {
-    const values = valueProvider(workflowContext);
+    const values = await valueProvider(workflowContext);
     return filterAndSortCompletionOptions(values, existingValues);
   }
 
diff --git a/actions-languageservice/src/validate.test.ts b/actions-languageservice/src/validate.test.ts
index 06616e0..ce230e6 100644
--- a/actions-languageservice/src/validate.test.ts
+++ b/actions-languageservice/src/validate.test.ts
@@ -1,6 +1,7 @@
-import {Diagnostic} from "vscode-languageserver-types";
+import {Diagnostic, DiagnosticSeverity} from "vscode-languageserver-types";
 import {createDocument} from "./test-utils/document";
 import {validate} from "./validate";
+import {defaultValueProviders} from "./value-providers/default";
 
 describe("validation", () => {
   it("valid workflow", async () => {
@@ -57,4 +58,68 @@ jobs:
       }
     } as Diagnostic);
   });
+
+  it("single value not returned by value provider", async () => {
+    const result = await validate(
+      createDocument(
+        "wf.yaml",
+        `on: push
+jobs:
+  build:
+    runs-on: does-not-exist
+    steps:
+    - run: echo`
+      ),
+      defaultValueProviders
+    );
+
+    expect(result.length).toBe(1);
+    expect(result[0]).toEqual({
+      message: "Value 'does-not-exist' is not valid",
+      severity: DiagnosticSeverity.Error,
+      range: {
+        end: {
+          character: 27,
+          line: 3
+        },
+        start: {
+          character: 13,
+          line: 3
+        }
+      }
+    } as Diagnostic);
+  });
+
+  it("value in sequence not returned by value provider", async () => {
+    const result = await validate(
+      createDocument(
+        "wf.yaml",
+        `on: push
+jobs:
+  build:
+    runs-on:
+    - ubuntu-latest
+    - does-not-exist
+    steps:
+    - run: echo`
+      ),
+      defaultValueProviders
+    );
+
+    expect(result.length).toBe(1);
+    expect(result[0]).toEqual({
+      message: "Value 'does-not-exist' is not valid",
+      severity: DiagnosticSeverity.Error,
+      range: {
+        end: {
+          character: 20,
+          line: 5
+        },
+        start: {
+          character: 6,
+          line: 5
+        }
+      }
+    } as Diagnostic);
+  });
 });
diff --git a/actions-languageservice/src/validate.ts b/actions-languageservice/src/validate.ts
index 36a7afc..89683a1 100644
--- a/actions-languageservice/src/validate.ts
+++ b/actions-languageservice/src/validate.ts
@@ -10,6 +10,8 @@ import {
   WorkflowTemplate
 } from "@github/actions-workflow-parser";
 import {splitAllowedContext} from "@github/actions-workflow-parser/templates/allowed-context";
+import {BasicExpressionToken} from "@github/actions-workflow-parser/templates/tokens/basic-expression-token";
+import {StringToken} from "@github/actions-workflow-parser/templates/tokens/string-token";
 import {TemplateToken} from "@github/actions-workflow-parser/templates/tokens/template-token";
 import {TokenRange} from "@github/actions-workflow-parser/templates/tokens/token-range";
 import {File} from "@github/actions-workflow-parser/workflows/file";
@@ -50,13 +52,15 @@ export async function validate(
       // Errors will be updated in the context
       const template = convertWorkflowTemplate(result.context, result.value);
 
-      // Validate with value providers
-      if (valueProviderConfig) {
-        await validateValueProviders(diagnostics, textDocument.uri, template, result, valueProviderConfig);
-      }
-
-      // Validate expressions
-      validateExpressions(diagnostics, result, contextProviderConfig);
+      // Validate expressions and value providers
+      await additionalValidations(
+        diagnostics,
+        textDocument.uri,
+        template,
+        result.value,
+        valueProviderConfig,
+        contextProviderConfig
+      );
     }
 
     // For now map parser errors directly to diagnostics
@@ -101,86 +105,34 @@ function mapRange(range: TokenRange | undefined): Range {
   };
 }
 
-function validateExpressions(
-  diagnostics: Diagnostic[],
-  result: ParseWorkflowResult,
-  contextProviderConfig: ContextProviderConfig | undefined
-) {
-  if (!result.value) {
-    return;
-  }
-
-  // Iterate over the parsed workflow
-  for (const token of TemplateToken.traverse(result.value)) {
-    if (isBasicExpression(token)) {
-      // Validate the expression
-      for (const expression of token.originalExpressions || [token]) {
-        const allowedContexts = token.definition?.readerContext || [];
-        const {namedContexts, functions} = splitAllowedContext(allowedContexts);
-
-        let expr: Expr | undefined;
-
-        try {
-          const l = new Lexer(expression.expression);
-          const lr = l.lex();
-
-          const p = new Parser(lr.tokens, namedContexts, functions);
-          expr = p.parse();
-        } catch {
-          // Ignore any error here, we should've caught this earlier in the parsing process
-          continue;
-        }
-
-        try {
-          const context = getContext(namedContexts, contextProviderConfig);
-
-          const e = new Evaluator(expr, wrapDictionary(context));
-          e.evaluate();
-
-          // Any invalid context access would've thrown an error via the `ErrorDictionary`, for now we don't have to check the actual
-          // result of the evaluation.
-        } catch (e) {
-          if (e instanceof AccessError) {
-            diagnostics.push({
-              message: `Context access might be invalid: ${e.keyName}`,
-              severity: DiagnosticSeverity.Warning,
-              range: mapRange(expression.range)
-            });
-          } else {
-            // Ignore error
-          }
-        }
-      }
-    }
-  }
-}
-
-async function validateValueProviders(
+async function additionalValidations(
   diagnostics: Diagnostic[],
   documentUri: URI,
   template: WorkflowTemplate,
-  result: ParseWorkflowResult,
-  valueProviderConfig: ValueProviderConfig
+  root: TemplateToken,
+  valueProviderConfig: ValueProviderConfig | undefined,
+  contextProviderConfig: ContextProviderConfig | undefined
 ) {
-  if (!result.value) {
-    return;
-  }
+  for (const token of TemplateToken.traverse(root)) {
+    // If this is an expression, validate it
+    if (isBasicExpression(token)) {
+      validateExpression(diagnostics, token, contextProviderConfig);
+    }
 
-  // Allowed values coming from the schema have already been validated. Only check if
-  // a value provider is defined for a token and if it is, validate the values match.
-  for (const token of TemplateToken.traverse(result.value)) {
-    if (token.range && token.definition?.key) {
+    // Allowed values coming from the schema have already been validated. Only check if
+    // a value provider is defined for a token and if it is, validate the values match.
+    if (valueProviderConfig && token.range && token.definition?.key) {
       const defKey = token.definition.key;
 
       let customValues: Value[] | undefined;
 
       const customValueProvider = valueProviderConfig[defKey];
       if (customValueProvider) {
-        customValues = await customValueProvider(getProviderContext(documentUri, template, result.value, token));
+        customValues = await customValueProvider(getProviderContext(documentUri, template, root, token));
       } else {
         const defaultValueProvider = defaultValueProviders[defKey];
         if (defaultValueProvider) {
-          customValues = defaultValueProvider(getProviderContext(documentUri, template, result.value, token));
+          customValues = await defaultValueProvider(getProviderContext(documentUri, template, root, token));
         }
       }
 
@@ -191,11 +143,7 @@ async function validateValueProviders(
 
             if (isString(entry)) {
               if (!customValues.map(x => x.label).includes(entry.value)) {
-                diagnostics.push({
-                  message: `Value '${entry.value}' is not allowed`,
-                  severity: DiagnosticSeverity.Error,
-                  range: mapRange(entry.range)
-                });
+                invalidValue(diagnostics, entry);
               }
             }
           }
@@ -203,11 +151,7 @@ async function validateValueProviders(
 
         if (isString(token)) {
           if (!customValues.map(x => x.label).includes(token.value)) {
-            diagnostics.push({
-              message: `Value '${token.value}' is not allowed`,
-              severity: DiagnosticSeverity.Error,
-              range: mapRange(token.range)
-            });
+            invalidValue(diagnostics, token);
           }
         }
       }
@@ -215,6 +159,14 @@ async function validateValueProviders(
   }
 }
 
+function invalidValue(diagnostics: Diagnostic[], token: StringToken) {
+  diagnostics.push({
+    message: `Value '${token.value}' is not valid`,
+    severity: DiagnosticSeverity.Error,
+    range: mapRange(token.range)
+  });
+}
+
 function getProviderContext(
   documentUri: URI,
   template: WorkflowTemplate,
@@ -230,3 +182,48 @@ function getProviderContext(
   );
   return getWorkflowContext(documentUri, template, path);
 }
+
+function validateExpression(
+  diagnostics: Diagnostic[],
+  token: BasicExpressionToken,
+  contextProviderConfig: ContextProviderConfig | undefined
+) {
+  // Validate the expression
+  for (const expression of token.originalExpressions || [token]) {
+    const allowedContexts = token.definition?.readerContext || [];
+    const {namedContexts, functions} = splitAllowedContext(allowedContexts);
+
+    let expr: Expr | undefined;
+
+    try {
+      const l = new Lexer(expression.expression);
+      const lr = l.lex();
+
+      const p = new Parser(lr.tokens, namedContexts, functions);
+      expr = p.parse();
+    } catch {
+      // Ignore any error here, we should've caught this earlier in the parsing process
+      continue;
+    }
+
+    try {
+      const context = getContext(namedContexts, contextProviderConfig);
+
+      const e = new Evaluator(expr, wrapDictionary(context));
+      e.evaluate();
+
+      // Any invalid context access would've thrown an error via the `ErrorDictionary`, for now we don't have to check the actual
+      // result of the evaluation.
+    } catch (e) {
+      if (e instanceof AccessError) {
+        diagnostics.push({
+          message: `Context access might be invalid: ${e.keyName}`,
+          severity: DiagnosticSeverity.Warning,
+          range: mapRange(expression.range)
+        });
+      } else {
+        // Ignore error
+      }
+    }
+  }
+}
diff --git a/actions-languageservice/src/value-providers/default.ts b/actions-languageservice/src/value-providers/default.ts
index 969833d..1b4c877 100644
--- a/actions-languageservice/src/value-providers/default.ts
+++ b/actions-languageservice/src/value-providers/default.ts
@@ -1,10 +1,10 @@
 import {WorkflowContext} from "../context/workflow-context";
-import {Value} from "./config";
+import {Value, ValueProviderConfig} from "./config";
 import {needs} from "./needs";
 
-export const defaultValueProviders: {[key: string]: (workflowContext: WorkflowContext) => Value[]} = {
+export const defaultValueProviders: ValueProviderConfig = {
   needs,
-  "runs-on": () =>
+  "runs-on": async (_: WorkflowContext) =>
     stringsToValues([
       "ubuntu-latest",
       "ubuntu-18.04",
diff --git a/actions-languageservice/src/value-providers/needs.ts b/actions-languageservice/src/value-providers/needs.ts
index 5ca3631..8c886b0 100644
--- a/actions-languageservice/src/value-providers/needs.ts
+++ b/actions-languageservice/src/value-providers/needs.ts
@@ -1,7 +1,7 @@
 import {WorkflowContext} from "../context/workflow-context";
 import {Value} from "./config";
 
-export function needs(context: WorkflowContext): Value[] {
+export async function needs(context: WorkflowContext): Promise<Value[]> {
   if (!context.template) {
     return [];
   }