diff --git a/util/pcie-defs.h b/util/pcie-defs.h
index 04c9ebd..ce114ba 100644
--- a/util/pcie-defs.h
+++ b/util/pcie-defs.h
@@ -31,6 +31,9 @@ struct pcie_bars {
     pthread_mutex_t locks[NUM_LOCKS];
 
     FILE *fserport;
+
+    /* fd holding OFD-owned lock for BAR resource files */
+    int fd_lock;
 };
 
 #endif
diff --git a/util/pcie-open.cc b/util/pcie-open.cc
index 744db2a..e56813e 100644
--- a/util/pcie-open.cc
+++ b/util/pcie-open.cc
@@ -28,6 +28,27 @@ void configure_mutexes(struct pcie_bars &bars)
             throw std::runtime_error("couldn't initialize mutex");
 }
 
+void lock_file(int fd)
+{
+    struct flock arg = {
+        /* exclusive lock */
+        .l_type = F_WRLCK,
+        /* lock the whole file */
+        .l_whence = SEEK_SET,
+        .l_start = 0,
+        .l_len = 0,
+        /* application is resposible for setting to 0 */
+        .l_pid = 0,
+    };
+    if (fcntl(fd, F_OFD_SETLK, &arg) < 0) {
+        /* allow program to work when F_OFD_SETLK isn't implemented */
+        if (errno == EINVAL)
+            fputs("WARNING: F_OFD_SETLK not supported!\n", stderr);
+        else
+            throw std::runtime_error(std::string("couldn't lock file"));
+    }
+}
+
 }
 
 void dev_open_slot(struct pcie_bars &bars, int slot)
@@ -69,6 +90,12 @@ void dev_open(struct pcie_bars &bars, const char *pci_address)
             if (fd < 0)
                 throw std::runtime_error(std::string("couldn't open resource file: ") + pci_address);
         }
+
+        if (bar == 0) {
+            lock_file(fd);
+            bars.fd_lock = fd;
+        }
+
         struct stat st;
         fstat(fd, &st);
         bars.sizes[i] = st.st_size;
@@ -130,6 +157,8 @@ void dev_close(struct pcie_bars &bars)
         return;
     }
 
+    close(bars.fd_lock);
+
     auto unmap = [&bars](auto &p, unsigned i) {
         munmap(const_cast<void *>(p), bars.sizes[i]);
         p = 0;