diff --git a/nsprpub/config/AIX.mk b/nsprpub/config/AIX.mk
index 3c64804d4baa..0df9d2db53a6 100644
--- a/nsprpub/config/AIX.mk
+++ b/nsprpub/config/AIX.mk
@@ -134,6 +134,10 @@ ifeq ($(OS_RELEASE),4.3)
 OS_CFLAGS	+= -DHAVE_SOCKLEN_T
 endif
 
+ifneq (,$(filter-out 3.2 4.1 4.2,$(OS_RELEASE)))
+OS_CFLAGS	+= -DHAVE_FCNTL_FILE_LOCKING
+endif
+
 ifeq (,$(filter-out 4.2 4.3,$(OS_RELEASE)))
 # On these OS revisions, localtime_r() is declared if _THREAD_SAFE
 # is defined.
diff --git a/nsprpub/config/HP-UX.mk b/nsprpub/config/HP-UX.mk
index 475bb155173a..63208618a508 100644
--- a/nsprpub/config/HP-UX.mk
+++ b/nsprpub/config/HP-UX.mk
@@ -143,7 +143,7 @@ ifeq ($(OS_RELEASE),B.11.00)
 			COMPILER_TAG    = _32
 		endif
 	endif
-OS_CFLAGS		+= -DHPUX10 -DHPUX11 -D_LARGEFILE64_SOURCE -D_PR_HAVE_OFF64_T
+OS_CFLAGS		+= -DHPUX10 -DHPUX11 -D_LARGEFILE64_SOURCE -D_PR_HAVE_OFF64_T -DHAVE_FCNTL_FILE_LOCKING
 DEFAULT_IMPL_STRATEGY = _PTH
 endif
 
diff --git a/nsprpub/config/IRIX.mk b/nsprpub/config/IRIX.mk
index 46e568055098..8620ea6590dc 100644
--- a/nsprpub/config/IRIX.mk
+++ b/nsprpub/config/IRIX.mk
@@ -116,7 +116,7 @@ else
 	endif
 endif
 
-ODD_CFLAGS		+= -DSVR4 -DIRIX
+ODD_CFLAGS		+= -DSVR4 -DIRIX -DHAVE_FCNTL_FILE_LOCKING
 
 CPU_ARCH		= mips
 
diff --git a/nsprpub/config/Linux.mk b/nsprpub/config/Linux.mk
index daad17f5b52b..eabdb5b1433b 100644
--- a/nsprpub/config/Linux.mk
+++ b/nsprpub/config/Linux.mk
@@ -82,7 +82,7 @@ OS_INCLUDES		=
 G++INCLUDES		= -I/usr/include/g++
 
 PLATFORM_FLAGS		= -ansi -Wall -pipe -DLINUX -Dlinux
-PORT_FLAGS		= -D_POSIX_SOURCE -D_BSD_SOURCE -D_SVID_SOURCE -DHAVE_STRERROR
+PORT_FLAGS		= -D_POSIX_SOURCE -D_BSD_SOURCE -D_SVID_SOURCE -DHAVE_STRERROR -DHAVE_FCNTL_FILE_LOCKING
 
 OS_CFLAGS		= $(DSO_CFLAGS) $(PLATFORM_FLAGS) $(PORT_FLAGS)
 
diff --git a/nsprpub/config/OSF1.mk b/nsprpub/config/OSF1.mk
index 5a80c457f965..ad97558b5ae8 100644
--- a/nsprpub/config/OSF1.mk
+++ b/nsprpub/config/OSF1.mk
@@ -96,6 +96,10 @@ ifneq (,$(filter-out V2.0 V3.2,$(OS_RELEASE)))
 OS_CFLAGS		+= -DOSF1_HAVE_MACHINE_BUILTINS_H
 endif
 
+ifneq (,$(filter-out V2.0 V3.2,$(OS_RELEASE)))
+OS_CFLAGS		+= -DHAVE_FCNTL_FILE_LOCKING
+endif
+
 ifeq (,$(filter-out V2.0 V3.2,$(OS_RELEASE)))
 OS_CFLAGS		+= -DHAVE_INT_LOCALTIME_R
 else
diff --git a/nsprpub/config/SunOS5.mk b/nsprpub/config/SunOS5.mk
index af7973fdee24..176028343767 100644
--- a/nsprpub/config/SunOS5.mk
+++ b/nsprpub/config/SunOS5.mk
@@ -109,7 +109,7 @@ endif
 
 RANLIB			= echo
 
-OS_DEFINES		= -DSVR4 -DSYSV -D__svr4 -D__svr4__ -DSOLARIS
+OS_DEFINES		= -DSVR4 -DSYSV -D__svr4 -D__svr4__ -DSOLARIS -DHAVE_FCNTL_FILE_LOCKING
 
 ifeq ($(OS_TEST),i86pc)
 CPU_ARCH		= x86
diff --git a/nsprpub/pr/src/md/unix/unix.c b/nsprpub/pr/src/md/unix/unix.c
index 1a9d25362866..ad97f4699dbc 100644
--- a/nsprpub/pr/src/md/unix/unix.c
+++ b/nsprpub/pr/src/md/unix/unix.c
@@ -3305,6 +3305,9 @@ _MD_LockFile(PRInt32 f)
     struct flock arg;
 
     arg.l_type = F_WRLCK;
+    arg.l_whence = SEEK_SET;
+    arg.l_start = 0;
+    arg.l_len = 0;  /* until EOF */
     rv = fcntl(f, F_SETLKW, &arg);
     if (rv == 0)
         return PR_SUCCESS;
@@ -3319,6 +3322,9 @@ _MD_TLockFile(PRInt32 f)
     struct flock arg;
 
     arg.l_type = F_WRLCK;
+    arg.l_whence = SEEK_SET;
+    arg.l_start = 0;
+    arg.l_len = 0;  /* until EOF */
     rv = fcntl(f, F_SETLK, &arg);
     if (rv == 0)
         return PR_SUCCESS;
@@ -3333,6 +3339,9 @@ _MD_UnlockFile(PRInt32 f)
     struct flock arg;
 
     arg.l_type = F_UNLCK;
+    arg.l_whence = SEEK_SET;
+    arg.l_start = 0;
+    arg.l_len = 0;  /* until EOF */
     rv = fcntl(f, F_SETLK, &arg);
     if (rv == 0)
         return PR_SUCCESS;