diff --git a/src/common/string.cpp b/src/common/string.cpp
index 622da992a2..0af2b0d885 100644
--- a/src/common/string.cpp
+++ b/src/common/string.cpp
@@ -2060,17 +2060,6 @@ static int DoStringPrintfV(wxString& str,
         // buffer were large enough (newer standards such as Unix98)
         if ( len < 0 )
         {
-            // NB: wxVsnprintf() may call either wxCRT_VsnprintfW or
-            //     wxCRT_VsnprintfA in UTF-8 build; wxUSE_WXVSNPRINTF
-            //     is true if *both* of them use our own implementation,
-            //     otherwise we can't be sure
-#if wxUSE_WXVSNPRINTF
-            // we know that our own implementation of wxVsnprintf() returns -1
-            // only for a format error - thus there's something wrong with
-            // the user's format string
-            buf[0] = '\0';
-            return -1;
-#else // possibly using system version
             // assume it only returns error if there is not enough space, but
             // as we don't know how much we need, double the current size of
             // the buffer
@@ -2082,16 +2071,9 @@ static int DoStringPrintfV(wxString& str,
             // still not enough, as we don't know how much we need, double the
             // current size of the buffer
                 size *= 2;
-#endif // wxUSE_WXVSNPRINTF/!wxUSE_WXVSNPRINTF
         }
         else if ( len >= size )
         {
-#if wxUSE_WXVSNPRINTF
-            // we know that our own implementation of wxVsnprintf() returns
-            // size+1 when there's not enough space but that's not the size
-            // of the required buffer!
-            size *= 2;      // so we just double the current size of the buffer
-#else
             // some vsnprintf() implementations NUL-terminate the buffer and
             // some don't in len == size case, to be safe always add 1
             // FIXME: I don't quite understand this comment.  The vsnprintf
@@ -2100,7 +2082,6 @@ static int DoStringPrintfV(wxString& str,
             // So OF COURSE you need to add 1 to get the right buffer size.
             // The following line is definitely correct, no question.
             size = len + 1;
-#endif
         }
         else // ok, there was enough space
         {
diff --git a/src/common/wxprintf.cpp b/src/common/wxprintf.cpp
index bc022d421e..06787963a2 100644
--- a/src/common/wxprintf.cpp
+++ b/src/common/wxprintf.cpp
@@ -25,6 +25,7 @@
 
 #include "wx/private/wxprintf.h"
 
+#include <errno.h>
 
 // ============================================================================
 // printf() implementation
@@ -106,6 +107,9 @@ static int wxDoVsnprintf(CharType *buf, size_t lenMax,
     if (parser.posarg_present && parser.nonposarg_present)
     {
         buf[0] = 0;
+        // Indicate to the caller that it's an unrecoverable error and not just
+        // due to the buffer being too small.
+        errno = EINVAL;
         return -1;      // format strings with both positional and
     }                   // non-positional conversion specifier are unsupported !!
 
@@ -131,6 +135,7 @@ static int wxDoVsnprintf(CharType *buf, size_t lenMax,
     if (!ok)
     {
         buf[0] = 0;
+        errno = EINVAL;
         return -1;
     }
 
@@ -154,7 +159,7 @@ static int wxDoVsnprintf(CharType *buf, size_t lenMax,
         if (lenCur == lenMax)
         {
             buf[lenMax - 1] = 0;
-            return lenMax+1;      // not enough space in the output buffer !
+            return -1;      // not enough space in the output buffer !
         }
 
         // process this specifier directly in the output buffer
@@ -163,7 +168,7 @@ static int wxDoVsnprintf(CharType *buf, size_t lenMax,
         if (n == -1)
         {
             buf[lenMax-1] = wxT('\0');  // be sure to always NUL-terminate the string
-            return lenMax+1;      // not enough space in the output buffer !
+            return -1;      // not enough space in the output buffer !
         }
         lenCur += n;
 
@@ -183,7 +188,7 @@ static int wxDoVsnprintf(CharType *buf, size_t lenMax,
     if (buf[lenCur])
     {
         buf[lenCur] = 0;
-        return lenMax+1;     // not enough space in the output buffer !
+        return -1;     // not enough space in the output buffer !
     }
 
     // Don't do:
diff --git a/tests/strings/vsnprintf.cpp b/tests/strings/vsnprintf.cpp
index ccc43f77ba..53f48c3e2e 100644
--- a/tests/strings/vsnprintf.cpp
+++ b/tests/strings/vsnprintf.cpp
@@ -52,11 +52,10 @@ int r;
 // Another helper which takes the size explicitly instead of using MAX_TEST_LEN
 //
 // NOTE: this macro is used also with too-small buffers (see Miscellaneous())
-//       test function, thus the return value can be > size and thus we
+//       test function, thus the return value can be either -1 or > size and we
 //       cannot check if r == (int)wxStrlen(buf)
 #define CMPTOSIZE(buffer, size, failuremsg, expected, fmt, ...) \
     r=wxSnprintf(buffer, size, fmt, ##__VA_ARGS__);             \
-    CHECK( r > 0 );                                             \
     INFO(failuremsg);                                           \
     CHECK( buffer == wxString(expected).Left(size - 1) )
 
@@ -340,8 +339,10 @@ TEST_CASE_METHOD(VsnprintfTestCase, "Vsnprintf::WrongFormatStrings", "[vsnprintf
             wxSnprintf(buf, MAX_TEST_LEN, wxT("%1$d %3$d"), 1, 2, 3) );
 
     // positional and non-positionals in the same format string:
+    errno = 0;
     r = wxSnprintf(buf, MAX_TEST_LEN, wxT("%1$d %d %3$d"), 1, 2, 3);
     CHECK( r == -1 );
+    CHECK( errno == EINVAL );
 }
 
 // BigToSmallBuffer() test case helper:
@@ -392,7 +393,6 @@ void VsnprintfTestCase::DoBigToSmallBuffer(T *buffer, int size)
     wxString expected =
         wxString(wxT("unicode string/char: unicode/U -- ansi string/char: ansi/A")).Left(size - 1);
 
-    CHECK( r != -1 );
     CHECK( expected == buffer );
 }