diff --git a/src/hal/hal.cpp b/src/hal/hal.cpp
index 62271b49..d1f16e8a 100644
--- a/src/hal/hal.cpp
+++ b/src/hal/hal.cpp
@@ -109,14 +109,17 @@ static void hal_io_check() {
 // Interrupt handlers
 static ostime_t interrupt_time[NUM_DIO] = {0};
 
+LMIC_ISR_ATTR
 static void hal_isrPin0() {
     ostime_t now = os_getTime();
     interrupt_time[0] = now ? now : 1;
 }
+LMIC_ISR_ATTR
 static void hal_isrPin1() {
     ostime_t now = os_getTime();
     interrupt_time[1] = now ? now : 1;
 }
+LMIC_ISR_ATTR
 static void hal_isrPin2() {
     ostime_t now = os_getTime();
     interrupt_time[2] = now ? now : 1;
diff --git a/src/lmic/config.h b/src/lmic/config.h
index 8673b46a..cc14614e 100644
--- a/src/lmic/config.h
+++ b/src/lmic/config.h
@@ -212,4 +212,11 @@
 # define LMIC_ENABLE_arbitrary_clock_error 0	/* PARAM */
 #endif
 
+#if defined(ESP8266) || defined(ESP32)
+// functions called from an interrupt context need this attribute
+#define LMIC_ISR_ATTR ICACHE_RAM_ATTR
+#else
+#define LMIC_ISR_ATTR
+#endif
+
 #endif // _lmic_config_h_