diff --git a/Arduino.mk b/Arduino.mk
index 767f493..508c7ab 100644
--- a/Arduino.mk
+++ b/Arduino.mk
@@ -836,7 +836,7 @@ endif
 get_monitor_port = $(if $(wildcard $(DEVICE_PATH)),$(firstword $(wildcard $(DEVICE_PATH))),$(error Arduino port $(DEVICE_PATH) not found!))
 
 # Returns the ISP port (first wildcard expansion) if it exists, otherwise it errors.
-get_isp_port = $(if $(wildcard $(ISP_PORT)),$(firstword $(wildcard $(ISP_PORT))),$(error ISP port $(ISP_PORT) not found!))
+get_isp_port = $(if $(wildcard $(ISP_PORT)),$(firstword $(wildcard $(ISP_PORT))),$(if $(findstring Xusb,X$(ISP_PORT)),$(ISP_PORT),$(error ISP port $(ISP_PORT) not found!)))
 
 # Command for avr_size: do $(call avr_size,elffile,hexfile)
 ifneq (,$(findstring AVR,$(shell $(SIZE) --help)))
@@ -1075,8 +1075,12 @@ endif
 
 AVRDUDE_ISP_OPTS = -c $(ISP_PROG) -b $(AVRDUDE_ISP_BAUDRATE)
 
-ifneq ($(strip $(ISP_PROG)),$(filter $(ISP_PROG), usbasp usbtiny gpio))
-    AVRDUDE_ISP_OPTS += -P $(call get_isp_port)
+ifndef $(ISP_PORT)
+    ifneq ($(strip $(ISP_PROG)),$(filter $(ISP_PROG), usbasp usbtiny gpio))
+        AVRDUDE_ISP_OPTS += -P $(call get_isp_port)
+    endif
+else
+	AVRDUDE_ISP_OPTS += -P $(call get_isp_port)
 endif
 
 ifndef ISP_EEPROM
diff --git a/HISTORY.md b/HISTORY.md
index 469a835..a70ac82 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -13,6 +13,7 @@ I tried to give credit whenever possible. If I have missed anyone, kindly add it
 - Tweak: Add `OBJDIR` to `arduino-mk-vars.md` (https://github.com/tinyladi)
 - Tweak: *Beautify* `arduino-mk-vars.md` with code blocks. (https://github.com/tinyladi)
 - Fix: AVR tools paths for chipKIT in Linux. (https://github.com/peplin)
+- Fix: Consider usb or usb:... to be a valid ISP_PORT (https://github.com/geoffholden)
 
 ### 1.3.1 (2014-02-04)
 - Fix: BUNDLED_AVR_TOOLS_DIR is now set properly when using only arduino-core and not the whole arduino package. (https://github.com/sej7278)