diff --git a/NOVA/nova_defs.h b/NOVA/nova_defs.h
index 207c1c69..dfd18e03 100644
--- a/NOVA/nova_defs.h
+++ b/NOVA/nova_defs.h
@@ -1,6 +1,6 @@
 /* nova_defs.h: NOVA/Eclipse simulator definitions 
 
-   Copyright (c) 1993-2012, Robert M. Supnik
+   Copyright (c) 1993-2020, Robert M. Supnik
 
    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
@@ -23,6 +23,7 @@
    used in advertising or otherwise to promote the sale, use or other dealings
    in this Software without prior written authorization from Robert M Supnik.
 
+   05-Mar-20    RMS     Fixed USE_INT64 test for Eclipse (Mark Pizzolato)
    25-Mar-12    RMS     Added missing parameters to prototypes (Mark Pizzolato)
    22-May-10    RMS     Added check for 64b definitions
    04-Jul-07    BKR     BUSY/DONE/INTR "convenience" macros added,
@@ -51,7 +52,7 @@
 
 #include "sim_defs.h"                                   /* simulator defns */
 
-#if defined(USE_INT64) || defined(USE_ADDR64)
+#if (defined(USE_INT64) && !defined(ECLIPSE)) || defined(USE_ADDR64)
 #error "Nova does not support 64b values!"
 #endif
 
diff --git a/Visual Studio Projects/ECLIPSE.vcproj b/Visual Studio Projects/ECLIPSE.vcproj
index dafc0812..5c868c24 100644
--- a/Visual Studio Projects/ECLIPSE.vcproj	
+++ b/Visual Studio Projects/ECLIPSE.vcproj	
@@ -40,7 +40,7 @@
 				Name="VCCLCompilerTool"
 				Optimization="0"
 				AdditionalIncludeDirectories="../;../NOVA/"
-				PreprocessorDefinitions="_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS"
+				PreprocessorDefinitions="ECLIPSE;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS"
 				MinimalRebuild="true"
 				BasicRuntimeChecks="3"
 				RuntimeLibrary="1"
@@ -118,7 +118,7 @@
 				InlineFunctionExpansion="1"
 				OmitFramePointers="true"
 				AdditionalIncludeDirectories="../;../NOVA/"
-				PreprocessorDefinitions="_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS"
+				PreprocessorDefinitions="ECLIPSE;_CRT_NONSTDC_NO_WARNINGS;_CRT_SECURE_NO_WARNINGS"
 				StringPooling="true"
 				RuntimeLibrary="0"
 				EnableFunctionLevelLinking="true"
diff --git a/makefile b/makefile
index 4b15a522..35909971 100644
--- a/makefile
+++ b/makefile
@@ -595,7 +595,7 @@ ECLIPSE = ${NOVAD}/eclipse_cpu.c ${NOVAD}/eclipse_tt.c ${NOVAD}/nova_sys.c \
 	${NOVAD}/nova_dkp.c ${NOVAD}/nova_dsk.c ${NOVAD}/nova_lp.c \
 	${NOVAD}/nova_mta.c ${NOVAD}/nova_plt.c ${NOVAD}/nova_pt.c \
 	${NOVAD}/nova_clk.c ${NOVAD}/nova_tt1.c ${NOVAD}/nova_qty.c
-ECLIPSE_OPT = -I ${NOVAD} -DECLIPSE
+ECLIPSE_OPT = -I ${NOVAD} -DECLIPSE -DUSE_INT64
 
 
 PDP18BD = PDP18B