diff --git a/configure/CONFIG b/configure/CONFIG
index 1c1242858..df454b29b 100644
--- a/configure/CONFIG
+++ b/configure/CONFIG
@@ -16,6 +16,10 @@ ifneq ($(wildcard $(TOP)/configure/CONFIG_BASE_VERSION),)
   CONFIG = $(TOP)/configure
   BASE_TOP=YES
 else
+  ifneq ($(origin EPICS_BASE),file)
+    # Essential for the EPICS build system, see convertRelease.pl
+    $(error EPICS_BASE must be set in a configure/RELEASE file)
+  endif
   CONFIG ?= $(EPICS_BASE)/configure
 endif