diff --git a/gtk/gtkcsscalcvalue.c b/gtk/gtkcsscalcvalue.c
index e10e790b23..8a2741a89e 100644
--- a/gtk/gtkcsscalcvalue.c
+++ b/gtk/gtkcsscalcvalue.c
@@ -150,15 +150,6 @@ gtk_css_value_calc_equal (const GtkCssValue *value1,
   return TRUE;
 }
 
-static GtkCssValue *
-gtk_css_value_calc_transition (GtkCssValue *start,
-                               GtkCssValue *end,
-                               guint        property_id,
-                               double       progress)
-{
-  return NULL;
-}
-
 static void
 gtk_css_value_calc_print (const GtkCssValue *value,
                           GString           *string)
@@ -257,7 +248,7 @@ static const GtkCssNumberValueClass GTK_CSS_VALUE_CALC = {
     gtk_css_value_calc_free,
     gtk_css_value_calc_compute,
     gtk_css_value_calc_equal,
-    gtk_css_value_calc_transition,
+    gtk_css_number_value_transition,
     gtk_css_value_calc_print
   },
   gtk_css_value_calc_get,
diff --git a/gtk/gtkcssdimensionvalue.c b/gtk/gtkcssdimensionvalue.c
index 87efb7a6d6..92c2d99cda 100644
--- a/gtk/gtkcssdimensionvalue.c
+++ b/gtk/gtkcssdimensionvalue.c
@@ -167,21 +167,6 @@ gtk_css_value_dimension_equal (const GtkCssValue *number1,
          number1->value == number2->value;
 }
 
-static GtkCssValue *
-gtk_css_value_dimension_transition (GtkCssValue *start,
-                                 GtkCssValue *end,
-                                 guint        property_id,
-                                 double       progress)
-{
-  /* FIXME: This needs to be supported at least for percentages,
-   * but for that we kinda need to support calc(5px + 50%) */
-  if (start->unit != end->unit)
-    return NULL;
-
-  return gtk_css_dimension_value_new (start->value + (end->value - start->value) * progress,
-                                      start->unit);
-}
-
 static void
 gtk_css_value_dimension_print (const GtkCssValue *number,
                             GString           *string)
@@ -290,7 +275,7 @@ static const GtkCssNumberValueClass GTK_CSS_VALUE_DIMENSION = {
     gtk_css_value_dimension_free,
     gtk_css_value_dimension_compute,
     gtk_css_value_dimension_equal,
-    gtk_css_value_dimension_transition,
+    gtk_css_number_value_transition,
     gtk_css_value_dimension_print
   },
   gtk_css_value_dimension_get,
diff --git a/gtk/gtkcssnumbervalue.c b/gtk/gtkcssnumbervalue.c
index d685fda902..80239d6f4d 100644
--- a/gtk/gtkcssnumbervalue.c
+++ b/gtk/gtkcssnumbervalue.c
@@ -106,6 +106,25 @@ _gtk_css_number_value_new (double     value,
   return gtk_css_dimension_value_new (value, unit);
 }
 
+GtkCssValue *
+gtk_css_number_value_transition (GtkCssValue *start,
+                                 GtkCssValue *end,
+                                 guint        property_id,
+                                 double       progress)
+{
+  GtkCssValue *result, *mul_start, *mul_end;
+
+  mul_start = gtk_css_number_value_multiply (start, 1 - progress);
+  mul_end = gtk_css_number_value_multiply (end, progress);
+
+  result = gtk_css_number_value_add (mul_start, mul_end);
+
+  _gtk_css_value_unref (mul_start);
+  _gtk_css_value_unref (mul_end);
+
+  return result;
+}
+
 gboolean
 gtk_css_number_value_can_parse (GtkCssParser *parser)
 {
diff --git a/gtk/gtkcssnumbervalueprivate.h b/gtk/gtkcssnumbervalueprivate.h
index 7cb750f87c..ddded6674c 100644
--- a/gtk/gtkcssnumbervalueprivate.h
+++ b/gtk/gtkcssnumbervalueprivate.h
@@ -54,6 +54,10 @@ struct _GtkCssNumberValueClass {
 
 GtkCssValue *   _gtk_css_number_value_new           (double                  value,
                                                      GtkCssUnit              unit);
+GtkCssValue *   gtk_css_number_value_transition     (GtkCssValue            *start,
+                                                     GtkCssValue            *end,
+                                                     guint                   property_id,
+                                                     double                  progress);
 gboolean        gtk_css_number_value_can_parse      (GtkCssParser           *parser);
 GtkCssValue *   _gtk_css_number_value_parse         (GtkCssParser           *parser,
                                                      GtkCssNumberParseFlags  flags);
diff --git a/gtk/gtkcssvalue.c b/gtk/gtkcssvalue.c
index 97804157b3..b9755cf6c4 100644
--- a/gtk/gtkcssvalue.c
+++ b/gtk/gtkcssvalue.c
@@ -136,7 +136,9 @@ _gtk_css_value_transition (GtkCssValue *start,
   gtk_internal_return_val_if_fail (start != NULL, FALSE);
   gtk_internal_return_val_if_fail (end != NULL, FALSE);
 
-  if (start->class != end->class)
+  /* We compare functions here instead of classes so that number
+   * values can all transition to each other */
+  if (start->class->transition != end->class->transition)
     return NULL;
 
   return start->class->transition (start, end, property_id, progress);