diff --git a/elab_expr.cc b/elab_expr.cc
index 4fe9dadf9..b2f741d4d 100644
--- a/elab_expr.cc
+++ b/elab_expr.cc
@@ -3166,7 +3166,7 @@ unsigned PENumber::test_width(Design*, NetScope*, width_mode_t&mode)
       min_width_   = 1;
       signed_flag_ = value_->has_sign();
 
-      if ((mode < LOSSLESS) && !value_->has_len())
+      if ((mode < LOSSLESS) && !value_->has_len() && !value_->is_single())
             mode = LOSSLESS;
 
       return expr_width_;
diff --git a/lexor.lex b/lexor.lex
index 48ad58070..f254245ac 100644
--- a/lexor.lex
+++ b/lexor.lex
@@ -329,6 +329,14 @@ TU [munpf]
                         return BASED_NUMBER; }
 \'[sS]?[hH][ \t]*[0-9a-fA-FxzXZ_\?]+ { yylval.number = make_unsized_hex(yytext);
                               return BASED_NUMBER; }
+\'[01xzXZ] {
+      if (generation_flag < GN_VER2005_SV) {
+	    cerr << yylloc.text << ":" << yylloc.first_line << ": warning: "
+		 << "Using SystemVerilog 'N bit vector.  Use at least "
+		 << "-g2005-sv to remove this warning." << endl;
+      }
+      yylval.number = make_unsized_binary(yytext);
+      return BASED_NUMBER; }
 
 [0-9][0-9_]* {
       yylval.number = make_unsized_dec(yytext);
@@ -684,6 +692,7 @@ void lex_end_table()
 verinum*make_unsized_binary(const char*txt)
 {
       bool sign_flag = false;
+      bool single_flag = false;
       const char*ptr = txt;
       assert(*ptr == '\'');
       ptr += 1;
@@ -693,8 +702,13 @@ verinum*make_unsized_binary(const char*txt)
 	    ptr += 1;
       }
 
-      assert(tolower(*ptr) == 'b');
-      ptr += 1;
+      assert((tolower(*ptr) == 'b') || (generation_flag >= GN_VER2005_SV));
+      if (tolower(*ptr) == 'b') {
+	    ptr += 1;
+      } else {
+	    assert(sign_flag == false);
+	    single_flag = true;
+      }
 
       while (*ptr && ((*ptr == ' ') || (*ptr == '\t')))
 	    ptr += 1;
@@ -734,6 +748,7 @@ verinum*make_unsized_binary(const char*txt)
 
       verinum*out = new verinum(bits, size, false);
       out->has_sign(sign_flag);
+      out->is_single(single_flag);
       delete[]bits;
       return out;
 }
diff --git a/verinum.cc b/verinum.cc
index 1b576c224..0c4629e4a 100644
--- a/verinum.cc
+++ b/verinum.cc
@@ -43,12 +43,12 @@ extern "C" long int lround(double x)
 static verinum::V add_with_carry(verinum::V l, verinum::V r, verinum::V&c);
 
 verinum::verinum()
-: bits_(0), nbits_(0), has_len_(false), has_sign_(false), string_flag_(false)
+: bits_(0), nbits_(0), has_len_(false), has_sign_(false), is_single_(false), string_flag_(false)
 {
 }
 
 verinum::verinum(const V*bits, unsigned nbits, bool has_len__)
-: has_len_(has_len__), has_sign_(false), string_flag_(false)
+: has_len_(has_len__), has_sign_(false), is_single_(false), string_flag_(false)
 {
       nbits_ = nbits;
       bits_ = new V [nbits];
@@ -111,7 +111,7 @@ static string process_verilog_string_quotes(const string&str)
 }
 
 verinum::verinum(const string&s)
-: has_len_(true), has_sign_(false), string_flag_(true)
+: has_len_(true), has_sign_(false), is_single_(false), string_flag_(true)
 {
       string str = process_verilog_string_quotes(s);
       nbits_ = str.length() * 8;
@@ -149,7 +149,7 @@ verinum::verinum(const string&s)
 }
 
 verinum::verinum(verinum::V val, unsigned n, bool h)
-: has_len_(h), has_sign_(false), string_flag_(false)
+: has_len_(h), has_sign_(false), is_single_(false), string_flag_(false)
 {
       nbits_ = n;
       bits_ = new V[nbits_];
@@ -158,7 +158,7 @@ verinum::verinum(verinum::V val, unsigned n, bool h)
 }
 
 verinum::verinum(uint64_t val, unsigned n)
-: has_len_(true), has_sign_(false), string_flag_(false)
+: has_len_(true), has_sign_(false), is_single_(false), string_flag_(false)
 {
       nbits_ = n;
       bits_ = new V[nbits_];
@@ -171,7 +171,7 @@ verinum::verinum(uint64_t val, unsigned n)
 /* The second argument is not used! It is there to make this
  * constructor unique. */
 verinum::verinum(double val, bool)
-: has_len_(false), has_sign_(true), string_flag_(false)
+: has_len_(false), has_sign_(true), is_single_(false), string_flag_(false)
 {
       bool is_neg = false;
       double fraction;
@@ -281,6 +281,7 @@ verinum::verinum(const verinum&that)
       bits_ = new V[nbits_];
       has_len_ = that.has_len_;
       has_sign_ = that.has_sign_;
+      is_single_ = that.is_single_;
       for (unsigned idx = 0 ;  idx < nbits_ ;  idx += 1)
 	    bits_[idx] = that.bits_[idx];
 }
@@ -292,6 +293,7 @@ verinum::verinum(const verinum&that, unsigned nbits)
       bits_ = new V[nbits_];
       has_len_ = true;
       has_sign_ = that.has_sign_;
+      is_single_ = false;
 
       unsigned copy = nbits;
       if (copy > that.nbits_)
@@ -300,7 +302,7 @@ verinum::verinum(const verinum&that, unsigned nbits)
 	    bits_[idx] = that.bits_[idx];
 
       if (copy < nbits_) {
-	    if (has_sign_) {
+	    if (has_sign_ || that.is_single_) {
 		  for (unsigned idx = copy ;  idx < nbits_ ;  idx += 1)
 			bits_[idx] = bits_[idx-1];
 	    } else {
@@ -311,7 +313,7 @@ verinum::verinum(const verinum&that, unsigned nbits)
 }
 
 verinum::verinum(int64_t that)
-: has_len_(false), has_sign_(true), string_flag_(false)
+: has_len_(false), has_sign_(true), is_single_(false), string_flag_(false)
 {
       int64_t tmp;
 
@@ -348,6 +350,7 @@ verinum& verinum::operator= (const verinum&that)
 
       has_len_ = that.has_len_;
       has_sign_ = that.has_sign_;
+      is_single_ = that.is_single_;
       string_flag_ = that.string_flag_;
       return *this;
 }
@@ -570,9 +573,9 @@ verinum pad_to_width(const verinum&that, unsigned width)
       }
 
       verinum::V pad = that[that.len()-1];
-      if (pad==verinum::V1 && !that.has_sign())
+      if (pad==verinum::V1 && !that.has_sign() && !that.is_single())
 	    pad = verinum::V0;
-      if (that.has_len() && !that.has_sign()) {
+      if (that.has_len() && !that.has_sign() && !that.is_single()) {
 	    if (pad==verinum::Vx)
 		  pad = verinum::V0;
 	    if (pad==verinum::Vz)
@@ -606,9 +609,9 @@ verinum cast_to_width(const verinum&that, unsigned width)
       }
 
       verinum::V pad = that[that.len()-1];
-      if (pad==verinum::V1 && !that.has_sign())
+      if (pad==verinum::V1 && !that.has_sign() && !that.is_single())
 	    pad = verinum::V0;
-      if (that.has_len() && !that.has_sign()) {
+      if (that.has_len() && !that.has_sign() && !that.is_single()) {
 	    if (pad==verinum::Vx)
 		  pad = verinum::V0;
 	    if (pad==verinum::Vz)
diff --git a/verinum.h b/verinum.h
index acab1d673..24ea075d7 100644
--- a/verinum.h
+++ b/verinum.h
@@ -70,6 +70,10 @@ class verinum {
       bool has_sign(bool flag) { has_sign_ = flag; return has_sign_; }
       bool has_sign() const { return has_sign_; }
 
+        // A number "is single" if it comes from a SystemVerilog 'N bit vector
+      bool is_single(bool flag) { is_single_ = flag; return is_single_; }
+      bool is_single() const { return is_single_; }
+
 	// A number is "defined" if there are no x or z bits in its value.
       bool is_defined() const;
       bool is_zero() const;
@@ -103,6 +107,7 @@ class verinum {
       unsigned nbits_;
       bool has_len_;
       bool has_sign_;
+      bool is_single_;
 
 	// These are some convenience flags that help us do a better
 	// job of pretty-printing values.