diff --git a/bitcoin-qt.pro b/bitcoin-qt.pro
index 6c1c4a78c..8a6f9efeb 100644
--- a/bitcoin-qt.pro
+++ b/bitcoin-qt.pro
@@ -372,6 +372,8 @@ win32:!contains(MINGW_THREAD_BUGFIX, 0) {
 !win32:!macx {
     DEFINES += LINUX
     LIBS += -lrt
+    # _FILE_OFFSET_BITS=64 lets 32-bit fopen transparently support large files.
+    DEFINES += _FILE_OFFSET_BITS=64
 }
 
 macx:HEADERS += src/qt/macdockiconhandler.h
diff --git a/src/makefile.unix b/src/makefile.unix
index 14cf1b8fa..b52a0f8ae 100644
--- a/src/makefile.unix
+++ b/src/makefile.unix
@@ -7,7 +7,7 @@ USE_IPV6:=1
 
 LINK:=$(CXX)
 
-DEFS=-DBOOST_SPIRIT_THREADSAFE
+DEFS=-DBOOST_SPIRIT_THREADSAFE -D_FILE_OFFSET_BITS=64
 
 DEFS += $(addprefix -I,$(CURDIR) $(CURDIR)/obj $(BOOST_INCLUDE_PATH) $(BDB_INCLUDE_PATH) $(OPENSSL_INCLUDE_PATH))
 LIBS = $(addprefix -L,$(BOOST_LIB_PATH) $(BDB_LIB_PATH) $(OPENSSL_LIB_PATH))