diff --git a/libcxx/src/strstream.cpp b/libcxx/src/strstream.cpp
--- a/libcxx/src/strstream.cpp
+++ b/libcxx/src/strstream.cpp
@@ -230,94 +230,82 @@
 }
 
 strstreambuf::pos_type
-strstreambuf::seekoff(off_type __off, ios_base::seekdir __way, ios_base::openmode __which)
-{
-    off_type __p(-1);
+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;
-    bool legal = false;
-    switch (__way)
-    {
+    switch (__way) {
     case ios::beg:
     case ios::end:
-        if (pos_in || pos_out)
-            legal = true;
+        if (!pos_in && !pos_out)
+            return pos_type(off_type(-1));
         break;
     case ios::cur:
-        if (pos_in != pos_out)
-            legal = true;
+        if (pos_in == pos_out)
+            return pos_type(off_type(-1));
         break;
     }
+
     if (pos_in && gptr() == nullptr)
-        legal = false;
+        return pos_type(off_type(-1));
     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(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();
     }
-    return pos_type(__p);
+    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);
+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)
-    {
-        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;
-            }
-        }
+    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(__p);
+    return pos_type(newoff);
 }
 
 istrstream::~istrstream()