diff --git a/include/wx/private/wxprintf.h b/include/wx/private/wxprintf.h
index e16b9f4e40..f34d68495e 100644
--- a/include/wx/private/wxprintf.h
+++ b/include/wx/private/wxprintf.h
@@ -797,6 +797,7 @@ struct wxPrintfConvSpecParser
 
     wxPrintfConvSpecParser(const CharType *fmt)
     {
+        nspecs =
         nargs = 0;
         posarg_present =
         nonposarg_present = false;
@@ -817,7 +818,7 @@ struct wxPrintfConvSpecParser
                 continue;
             }
 
-            ConvSpec *spec = &specs[nargs];
+            ConvSpec *spec = &specs[nspecs];
             spec->Init();
 
             // attempt to parse this format specification
@@ -838,7 +839,7 @@ struct wxPrintfConvSpecParser
 
                 for ( unsigned n = 0; n < numAsterisks; n++ )
                 {
-                    if ( ++nargs == wxMAX_SVNPRINTF_ARGUMENTS )
+                    if ( ++nspecs == wxMAX_SVNPRINTF_ARGUMENTS )
                         break;
 
                     // TODO: we need to support specifiers of the form "%2$*1$s"
@@ -861,19 +862,19 @@ struct wxPrintfConvSpecParser
                         );
                     }
 
-                    specs[nargs] = *spec;
+                    specs[nspecs] = *spec;
 
                     // make an entry for '*' and point to it from pspec
                     spec->Init();
                     spec->m_type = wxPAT_STAR;
-                    pspec[nargs - 1] = spec;
+                    pspec[nargs++] = spec;
 
-                    spec = &specs[nargs];
+                    spec = &specs[nspecs];
                 }
 
                 // If we hit the maximal number of arguments inside the inner
                 // loop, break out of the outer one as well.
-                if ( nargs == wxMAX_SVNPRINTF_ARGUMENTS )
+                if ( nspecs == wxMAX_SVNPRINTF_ARGUMENTS )
                     break;
             }
 
@@ -884,25 +885,44 @@ struct wxPrintfConvSpecParser
                 // the positional arguments start from number 1 so we need
                 // to adjust the index
                 spec->m_pos--;
+
+                // We could be reusing an already existing argument, only
+                // increment their number if it's really a new one.
+                if ( spec->m_pos >= nargs )
+                {
+                    nargs = spec->m_pos + 1;
+                }
+                else if ( pspec[spec->m_pos] ) // Had we seen it before?
+                {
+                    // Check that the type specified this time is compatible
+                    // with the previously-specified type.
+                    wxASSERT_MSG
+                    (
+                        pspec[spec->m_pos]->m_type == spec->m_type,
+                        "Positional parameter specified multiple times "
+                        "with incompatible types."
+                    );
+                }
+
                 posarg_present = true;
             }
             else // not a positional argument...
             {
-                spec->m_pos = nargs;
+                spec->m_pos = nargs++;
                 nonposarg_present = true;
             }
 
             // this conversion specifier is tied to the pos-th argument...
             pspec[spec->m_pos] = spec;
 
-            if ( ++nargs == wxMAX_SVNPRINTF_ARGUMENTS )
+            if ( ++nspecs == wxMAX_SVNPRINTF_ARGUMENTS )
                 break;
         }
 
 
         // warn if we lost any arguments (the program probably will crash
         // anyhow because of stack corruption...)
-        if ( nargs == wxMAX_SVNPRINTF_ARGUMENTS )
+        if ( nspecs == wxMAX_SVNPRINTF_ARGUMENTS )
         {
             wxFAIL_MSG
             (
@@ -919,6 +939,10 @@ struct wxPrintfConvSpecParser
     }
 
     // total number of valid elements in specs
+    unsigned nspecs;
+
+    // total number of arguments, also number of valid elements in pspec, and
+    // always less than or (usually) equal to nspecs
     unsigned nargs;
 
     // all format specifications in this format string in order of their
diff --git a/src/common/wxprintf.cpp b/src/common/wxprintf.cpp
index 69cb20cbae..7e18b83e89 100644
--- a/src/common/wxprintf.cpp
+++ b/src/common/wxprintf.cpp
@@ -139,7 +139,7 @@ static int wxDoVsnprintf(CharType *buf, size_t lenMax,
 
     // finally, process each conversion specifier with its own argument
     const CharType *toparse = format;
-    for (i=0; i < parser.nargs; i++)
+    for (i=0; i < parser.nspecs; i++)
     {
         wxPrintfConvSpec<CharType>& spec = parser.specs[i];
 
diff --git a/tests/strings/strings.cpp b/tests/strings/strings.cpp
index bfcdb5e187..7e960ecb64 100644
--- a/tests/strings/strings.cpp
+++ b/tests/strings/strings.cpp
@@ -188,6 +188,8 @@ void StringTestCase::Format()
         "4 world hello world 3",
         wxString::Format("%4$d %2$s %1$s %2$s %3$d", "hello", "world", 3, 4)
     );
+
+    CHECK( wxString::Format("%1$o %1$d %1$x", 20) == "24 20 14" );
 }
 
 void StringTestCase::FormatUnicode()