diff --git a/src/Perl6/Actions.pm b/src/Perl6/Actions.pm
index a2e0efb9eee..a9e14b3af7e 100644
--- a/src/Perl6/Actions.pm
+++ b/src/Perl6/Actions.pm
@@ -2330,37 +2330,20 @@ method numish($/) {
 }
 
 method dec_number($/) {
-    my $int  := $<int> ?? $<int>.ast !! 0;
-    my $frac := $<frac> ?? $<frac>.ast !! 0;
-    my $base := Q:PIR {
-        $P0 = find_lex '$/'
-        $S0 = $P0['frac']
-        $I1 = length $S0
-        $I0 = 0
-        $I2 = 1
-      loop:
-        unless $I0 < $I1 goto done
-        $S1 = substr $S0, $I0, 1
-        inc $I0
-        if $S1 == '_' goto loop
-        $I2 *= 10
-        goto loop
-      done:
-        %r = box $I2
-    };
+    my $int  := $<int> ?? ~$<int> !! "0";
+    my $frac := $<frac> ?? ~$<frac> !! "0";
     if $<escale> {
-        my $exp := $<escale>[0]<decint>.ast;
-        if $<escale>[0]<sign> eq '-' { $exp := -$exp; }
-        make PAST::Val.new(
-            :value(($int * $base + $frac) / $base * 10 ** +$exp ) ,
-            :returns('Num')
+        my $exp := ~$<escale>[0]<decint>;
+        make PAST::Op.new(
+            :pasttype('call'),
+            PAST::Var.new(:scope('package'), :name('&str2num-num'), :namespace('Str')),
+             0, $int, $frac, ($<escale>[0]<sign> eq '-'), $exp
         );
-    }
-    else {
+    } else {
         make PAST::Op.new(
-            :pasttype('callmethod'), :name('new'),
-            PAST::Var.new( :name('Rat'), :namespace(''), :scope('package') ),
-            $int * $base + $frac, $base, :node($/)
+            :pasttype('call'),
+            PAST::Var.new(:scope('package'), :name('&str2num-rat'), :namespace('Str')),
+             0, $int, $frac
         );
     }
 }
diff --git a/src/core/Str.pm b/src/core/Str.pm
index 81aa9ec8427..cdee029f994 100644
--- a/src/core/Str.pm
+++ b/src/core/Str.pm
@@ -42,4 +42,81 @@ augment class Str does Stringy {
         };
         return Buf.new(@bytes);
     }
+
+    our sub str2num-int($src) {
+        Q:PIR {
+            .local pmc src
+            .local string src_s
+            src = find_lex '$src'
+            src_s = src
+            .local int pos, eos
+            .local num result
+            pos = 0
+            eos = length src_s
+            result = 0
+          str_loop:
+            unless pos < eos goto str_done
+            .local string char
+            char = substr src_s, pos, 1
+            if char == '_' goto str_next
+            .local int digitval
+            digitval = index "0123456789", char
+            if digitval < 0 goto err_base
+            if digitval >= 10 goto err_base
+            result *= 10
+            result += digitval
+          str_next:
+            inc pos
+            goto str_loop
+          err_base:
+        src.'panic'('Invalid radix conversion of "', char, '"')
+          str_done:
+            %r = box result
+        };
+    }
+
+    our sub str2num-base($src) {
+        Q:PIR {
+            .local pmc src
+            .local string src_s
+            src = find_lex '$src'
+            src_s = src
+            .local int pos, eos
+            .local num result
+            pos = 0
+            eos = length src_s
+            result = 1
+          str_loop:
+            unless pos < eos goto str_done
+            .local string char
+            char = substr src_s, pos, 1
+            if char == '_' goto str_next
+            result *= 10
+          str_next:
+            inc pos
+            goto str_loop
+          err_base:
+        src.'panic'('Invalid radix conversion of "', char, '"')
+          str_done:
+            %r = box result
+        };
+    }
+
+    our sub str2num-rat($negate, $int-part, $frac-part is copy) is export {
+        $frac-part.=subst(/(\d)0+$/, { ~$_[0] });
+        my $result = upgrade_to_num_if_needed(str2num-int($int-part))
+                     + upgrade_to_num_if_needed(str2num-int($frac-part))
+                       / upgrade_to_num_if_needed(str2num-base($frac-part));
+        $result = -$result if $negate;
+        $result;
+    }
+
+    our sub str2num-num($negate, $int-part, $frac-part, $exp-part-negate, $exp-part) is export {
+        my $exp = str2num-int($exp-part);
+        $exp = -$exp if $exp-part-negate;
+        my $result = (str2num-int($int-part) + str2num-int($frac-part) / str2num-base($frac-part))
+                     * 10 ** $exp;
+        $result = -$result if $negate;
+        $result;
+    }
 }