diff --git a/src/grovewfs/grovewfs.h b/src/grovewfs/grovewfs.h
index 382ecbf7..51227fbe 100644
--- a/src/grovewfs/grovewfs.h
+++ b/src/grovewfs/grovewfs.h
@@ -116,12 +116,6 @@ namespace upm {
      */
     uint32_t flowCounter() { return m_flowCounter; };
 
-    /**
-     * Flow interrupt service routine (ISR)
-     *
-     */
-    static void flowISR(void *ctx);
-
     /**
      * Computes the flow rate in liters per minute (LPM)
      *
@@ -130,6 +124,12 @@ namespace upm {
     float flowRate();
 
   private:
+    /**
+     * Flow interrupt service routine (ISR)
+     *
+     */
+    static void flowISR(void *ctx);
+
     volatile uint32_t m_flowCounter;
     struct timeval m_startTime;
     mraa_gpio_context m_gpio;