diff --git a/pkg/middleware/stored_session.go b/pkg/middleware/stored_session.go
index f861c756..c4b2b718 100644
--- a/pkg/middleware/stored_session.go
+++ b/pkg/middleware/stored_session.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"strings"
 	"time"
 
 	"github.com/justinas/alice"
@@ -31,6 +32,34 @@ const (
 	sessionRefreshRetryPeriod = 10 * time.Millisecond
 )
 
+// isFatalRefreshError checks if a refresh error indicates a revoked or
+// non-existent session that should be immediately invalidated.
+// Fatal errors indicate the session is no longer valid at the provider level.
+// Non-fatal errors (network issues, timeouts) should not invalidate the session.
+//
+// Only checks standard OAuth2 error codes (RFC 6749 Section 5.2).
+// Does NOT check error_description strings as they are optional and provider-specific.
+func isFatalRefreshError(err error) bool {
+	if err == nil {
+		return false
+	}
+
+	errStr := err.Error()
+	// Only check standard OAuth2 error codes (RFC 6749 Section 5.2)
+	// Do NOT check error_description strings as they are optional and provider-specific
+	fatalErrors := []string{
+		"invalid_grant",  // refresh token revoked, expired, or session terminated
+		"invalid_client", // client credentials no longer valid
+	}
+
+	for _, fe := range fatalErrors {
+		if strings.Contains(errStr, fe) {
+			return true
+		}
+	}
+	return false
+}
+
 // StoredSessionLoaderOptions contains all of the requirements to construct
 // a stored session loader.
 // All options must be provided.
@@ -188,9 +217,25 @@ func (s *storedSessionLoader) refreshSessionIfNeeded(rw http.ResponseWriter, req
 	// We are holding the lock and the session needs a refresh
 	logger.Printf("Refreshing session - User: %s; SessionAge: %s", session.User, session.Age())
 	if err := s.refreshSession(rw, req, session); err != nil {
-		// If a preemptive refresh fails, we still keep the session
-		// if validateSession succeeds.
 		logger.Errorf("Unable to refresh session: %v", err)
+
+		// Check if this is a fatal error that indicates the session is revoked
+		// or no longer valid at the provider level
+		if isFatalRefreshError(err) {
+			logger.Printf("Fatal refresh error detected (session revoked or invalid), clearing session for user: %s", session.User)
+
+			// Clear the session from storage (Redis) and remove the cookie
+			clearErr := s.store.Clear(rw, req)
+			if clearErr != nil {
+				logger.Errorf("Error clearing session: %v", clearErr)
+			}
+
+			// Return error immediately to force re-authentication
+			return fmt.Errorf("session invalidated due to fatal refresh error: %w", err)
+		}
+
+		// For non-fatal errors (network issues, timeouts), keep the session
+		// and let validateSession determine if it's still usable
 	}
 
 	// Validate all sessions after any Redeem/Refresh operation (fail or success)
diff --git a/pkg/middleware/stored_session_test.go b/pkg/middleware/stored_session_test.go
index d8e78f2f..c913a4ef 100644
--- a/pkg/middleware/stored_session_test.go
+++ b/pkg/middleware/stored_session_test.go
@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"sync"
+	"testing"
 	"time"
 
 	middlewareapi "github.com/oauth2-proxy/oauth2-proxy/v7/pkg/apis/middleware"
@@ -801,3 +802,53 @@ func (f *fakeSessionStore) Clear(rw http.ResponseWriter, req *http.Request) erro
 func (f *fakeSessionStore) VerifyConnection(_ context.Context) error {
 	return nil
 }
+
+// TestIsFatalRefreshError tests the isFatalRefreshError function to ensure
+// it correctly identifies fatal OAuth2 errors that should invalidate a session.
+func TestIsFatalRefreshError(t *testing.T) {
+	tests := []struct {
+		name     string
+		err      error
+		expected bool
+	}{
+		{
+			name:     "nil error",
+			err:      nil,
+			expected: false,
+		},
+		{
+			name:     "invalid_grant error",
+			err:      fmt.Errorf("failed to get token: oauth2: \"invalid_grant\" \"Session not active\""),
+			expected: true,
+		},
+		{
+			name:     "invalid_client error",
+			err:      fmt.Errorf("invalid_client: client not found"),
+			expected: true,
+		},
+		{
+			name:     "network timeout - not fatal",
+			err:      fmt.Errorf("Post \"https://keycloak/token\": dial tcp: connect: connection refused"),
+			expected: false,
+		},
+		{
+			name:     "server error - not fatal",
+			err:      fmt.Errorf("unexpected status code 500"),
+			expected: false,
+		},
+		{
+			name:     "generic refresh error - not fatal",
+			err:      fmt.Errorf("error refreshing tokens: context deadline exceeded"),
+			expected: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := isFatalRefreshError(tt.err)
+			if result != tt.expected {
+				t.Errorf("isFatalRefreshError(%v) = %v, want %v", tt.err, result, tt.expected)
+			}
+		})
+	}
+}