diff --git a/libcxx/src/strstream.cpp b/libcxx/src/strstream.cpp
--- a/libcxx/src/strstream.cpp
+++ b/libcxx/src/strstream.cpp
@@ -229,95 +229,81 @@
     return int_type(static_cast<unsigned char>(*gptr()));
 }
 
-strstreambuf::pos_type
-strstreambuf::seekoff(off_type __off, ios_base::seekdir __way, ios_base::openmode __which)
-{
-    off_type __p(-1);
-    bool pos_in = (__which & ios::in) != 0;
-    bool pos_out = (__which & ios::out) != 0;
-    bool legal = false;
-    switch (__way)
-    {
-    case ios::beg:
-    case ios::end:
-        if (pos_in || pos_out)
-            legal = true;
-        break;
-    case ios::cur:
-        if (pos_in != pos_out)
-            legal = true;
-        break;
-    }
-    if (pos_in && gptr() == nullptr)
-        legal = false;
-    if (pos_out && pptr() == nullptr)
-        legal = false;
-    if (legal)
-    {
-        off_type newoff;
-        char* seekhigh = epptr() ? epptr() : egptr();
-        switch (__way)
-        {
-        case ios::beg:
-            newoff = 0;
-            break;
-        case ios::cur:
-            newoff = (pos_in ? gptr() : pptr()) - eback();
-            break;
-        case ios::end:
-            newoff = seekhigh - eback();
-            break;
-        default:
-            _LIBCPP_UNREACHABLE();
-        }
-        newoff += __off;
-        if (0 <= newoff && newoff <= seekhigh - eback())
-        {
-            char* newpos = eback() + newoff;
-            if (pos_in)
-                setg(eback(), newpos, _VSTD::max(newpos, egptr()));
-            if (pos_out)
-            {
-                // min(pbase, newpos), newpos, epptr()
-                __off = epptr() - newpos;
-                setp(min(pbase(), newpos), epptr());
-                __pbump((epptr() - pbase()) - __off);
-            }
-            __p = newoff;
-        }
-    }
-    return pos_type(__p);
+strstreambuf::pos_type strstreambuf::seekoff(off_type __off, ios_base::seekdir __way, ios_base::openmode __which) {
+  bool pos_in = (__which & ios::in) != 0;
+  bool pos_out = (__which & ios::out) != 0;
+  switch (__way) {
+  case ios::beg:
+  case ios::end:
+    if (!pos_in && !pos_out)
+      return pos_type(off_type(-1));
+    break;
+  case ios::cur:
+    if (pos_in == pos_out)
+      return pos_type(off_type(-1));
+    break;
+  }
+
+  if (pos_in && gptr() == nullptr)
+    return pos_type(off_type(-1));
+  if (pos_out && pptr() == nullptr)
+    return pos_type(off_type(-1));
+
+  off_type newoff;
+  char* seekhigh = epptr() ? epptr() : egptr();
+  switch (__way) {
+  case ios::beg:
+    newoff = 0;
+    break;
+  case ios::cur:
+    newoff = (pos_in ? gptr() : pptr()) - eback();
+    break;
+  case ios::end:
+    newoff = seekhigh - eback();
+    break;
+  default:
+    _LIBCPP_UNREACHABLE();
+  }
+  newoff += __off;
+  if (newoff < 0 || newoff > seekhigh - eback())
+    return pos_type(off_type(-1));
+
+  char* newpos = eback() + newoff;
+  if (pos_in)
+    setg(eback(), newpos, _VSTD::max(newpos, egptr()));
+  if (pos_out) {
+    // min(pbase, newpos), newpos, epptr()
+    __off = epptr() - newpos;
+    setp(min(pbase(), newpos), epptr());
+    __pbump((epptr() - pbase()) - __off);
+  }
+  return pos_type(newoff);
 }
 
-strstreambuf::pos_type
-strstreambuf::seekpos(pos_type __sp, ios_base::openmode __which)
-{
-    off_type __p(-1);
-    bool pos_in = (__which & ios::in) != 0;
-    bool pos_out = (__which & ios::out) != 0;
-    if (pos_in || pos_out)
-    {
-        if (!((pos_in && gptr() == nullptr) || (pos_out && pptr() == nullptr)))
-        {
-            off_type newoff = __sp;
-            char* seekhigh = epptr() ? epptr() : egptr();
-            if (0 <= newoff && newoff <= seekhigh - eback())
-            {
-                char* newpos = eback() + newoff;
-                if (pos_in)
-                    setg(eback(), newpos, _VSTD::max(newpos, egptr()));
-                if (pos_out)
-                {
-                    // min(pbase, newpos), newpos, epptr()
-                    off_type temp = epptr() - newpos;
-                    setp(min(pbase(), newpos), epptr());
-                    __pbump((epptr() - pbase()) - temp);
-                }
-                __p = newoff;
-            }
-        }
-    }
-    return pos_type(__p);
+strstreambuf::pos_type strstreambuf::seekpos(pos_type __sp, ios_base::openmode __which) {
+  bool pos_in = (__which & ios::in) != 0;
+  bool pos_out = (__which & ios::out) != 0;
+  if (!pos_in && !pos_out)
+    return pos_type(off_type(-1));
+
+  if ((pos_in && gptr() == nullptr) || (pos_out && pptr() == nullptr))
+    return pos_type(off_type(-1));
+
+  off_type newoff = __sp;
+  char* seekhigh = epptr() ? epptr() : egptr();
+  if (newoff < 0 || newoff > seekhigh - eback())
+    return pos_type(off_type(-1));
+
+  char* newpos = eback() + newoff;
+  if (pos_in)
+    setg(eback(), newpos, _VSTD::max(newpos, egptr()));
+  if (pos_out) {
+    // min(pbase, newpos), newpos, epptr()
+    off_type temp = epptr() - newpos;
+    setp(min(pbase(), newpos), epptr());
+    __pbump((epptr() - pbase()) - temp);
+  }
+  return pos_type(newoff);
 }
 
 istrstream::~istrstream()