Index: clang/lib/Sema/Sema.cpp
===================================================================
--- clang/lib/Sema/Sema.cpp
+++ clang/lib/Sema/Sema.cpp
@@ -811,8 +811,22 @@
       // FIXME: We can promote this to an error. The function or variable can't
       // be defined anywhere else, so the program must necessarily violate the
       // one definition rule.
-      S.Diag(VD->getLocation(), diag::warn_undefined_internal)
-        << isa<VarDecl>(VD) << VD;
+      bool IsImplicitBase = false;
+      if (FunctionDecl *BaseD = dyn_cast<FunctionDecl>(VD)) {
+        OMPDeclareVariantAttr *DVAttr = BaseD->getAttr<OMPDeclareVariantAttr>();
+        if (DVAttr && !DVAttr->getTraitInfo().isExtensionActive(
+                          llvm::omp::TraitProperty::
+                              implementation_extension_disable_implicit_base)) {
+          FunctionDecl *Func = dyn_cast<FunctionDecl>(
+              cast<DeclRefExpr>(DVAttr->getVariantFuncRef())->getDecl());
+          IsImplicitBase =
+              BaseD->isImplicit() &&
+              Func->getName().str().find(BaseD->getName().str()) >= 0;
+        }
+      }
+      if (!S.getLangOpts().OpenMP || !IsImplicitBase)
+        S.Diag(VD->getLocation(), diag::warn_undefined_internal)
+            << isa<VarDecl>(VD) << VD;
     } else if (auto *FD = dyn_cast<FunctionDecl>(VD)) {
       (void)FD;
       assert(FD->getMostRecentDecl()->isInlined() &&
Index: clang/test/OpenMP/declare_variant.cpp
===================================================================
--- /dev/null
+++ clang/test/OpenMP/declare_variant.cpp
@@ -0,0 +1,31 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fopenmp -verify %s
+
+namespace {
+  // expected-warning@+1{{function '(anonymous namespace)::bar' has internal linkage but is not defined}}
+void bar();
+}
+
+#pragma omp begin declare variant match(user={condition(1)})
+void bar() {
+}
+#pragma omp end declare variant
+
+// expected-warning@+1{{function 'baz' has internal linkage but is not defined}}
+static void baz();
+#pragma omp begin declare variant match(device = {kind(nohost)})
+static void baz() {}
+#pragma omp end declare variant
+
+#pragma omp begin declare variant match(device = {kind(host)})
+static void foo() {}
+#pragma omp end declare variant
+
+int main() {
+  foo();
+// expected-note@+1{{used here}}
+  baz();
+// expected-note@+1{{used here}}
+  bar();
+
+  return 0;
+}