diff --git a/src/basicio.cpp b/src/basicio.cpp
index cf5d0381..2bf7cf7e 100644
--- a/src/basicio.cpp
+++ b/src/basicio.cpp
@@ -297,7 +297,9 @@ namespace Exiv2 {
         }
         p_->mappedLength_ = size();
         p_->isWriteable_ = isWriteable;
-        if (p_->isWriteable_ && p_->switchMode(Impl::opWrite) != 0) return 0;
+        if (p_->isWriteable_ && p_->switchMode(Impl::opWrite) != 0) {
+            throw Error(16, path(), strError());
+        }
 #if defined EXV_HAVE_MMAP && defined EXV_HAVE_MUNMAP
         int prot = PROT_READ;
         if (p_->isWriteable_) {
@@ -343,7 +345,9 @@ namespace Exiv2 {
 #else
         // Workaround for platforms without mmap: Read the file into memory
         DataBuf buf(static_cast<long>(p_->mappedLength_));
-        read(buf.pData_, buf.size_);
+        if (read(buf.pData_, buf.size_) != buf.size_) {
+            throw Error(2, path(), strError(), "FileIo::read");
+        }
         if (error() || eof()) throw Error(2, path(), strError(), "FileIo::mmap");
         p_->pMappedArea_ = buf.release().first;
         p_->isMalloced_ = true;
diff --git a/src/error.cpp b/src/error.cpp
index 02983135..b7ca49e3 100644
--- a/src/error.cpp
+++ b/src/error.cpp
@@ -67,7 +67,7 @@ namespace {
         { 13, N_("Image type %1 is not supported") }, // %1=image type
         { 14, N_("Failed to read image data") },
         { 15, N_("This does not look like a JPEG image") },
-//      { 16, N_("") }, -- currently not used
+        { 16, N_("%1: Failed to map file for reading and writing: %2") }, // %1=path, %2=strerror
         { 17, N_("%1: Failed to rename file to %2: %3") }, // %1=old path, %2=new path, %3=strerror
         { 18, N_("%1: Transfer failed: %2") }, // %1=path, %2=strerror
         { 19, N_("Memory transfer failed: %1") }, // %1=strerror