diff --git a/Lib/fontTools/varLib/instancer/__init__.py b/Lib/fontTools/varLib/instancer/__init__.py
index 77762979c..cde1d39f6 100644
--- a/Lib/fontTools/varLib/instancer/__init__.py
+++ b/Lib/fontTools/varLib/instancer/__init__.py
@@ -1287,6 +1287,9 @@ def instantiateVariableFont(
                     ignoreErrors=(overlap == OverlapMode.REMOVE_AND_IGNORE_ERRORS),
                 )
 
+    if "OS/2" in varfont:
+        varfont["OS/2"].recalcAvgCharWidth(varfont)
+
     varLib.set_default_weight_width_slant(
         varfont, location=axisLimits.defaultLocation()
     )
diff --git a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-100,100.ttx b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-100,100.ttx
index 776a92f18..c89949c25 100644
--- a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-100,100.ttx
+++ b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-100,100.ttx
@@ -74,7 +74,7 @@
     <!-- The fields 'usFirstCharIndex' and 'usLastCharIndex'
          will be recalculated by the compiler -->
     <version value="4"/>
-    <xAvgCharWidth value="577"/>
+    <xAvgCharWidth value="502"/>
     <usWeightClass value="100"/>
     <usWidthClass value="5"/>
     <fsType value="00000000 00000000"/>
diff --git a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-100,62.5.ttx b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-100,62.5.ttx
index 61bc41cc3..a78019f83 100644
--- a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-100,62.5.ttx
+++ b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-100,62.5.ttx
@@ -74,7 +74,7 @@
     <!-- The fields 'usFirstCharIndex' and 'usLastCharIndex'
          will be recalculated by the compiler -->
     <version value="4"/>
-    <xAvgCharWidth value="577"/>
+    <xAvgCharWidth value="383"/>
     <usWeightClass value="100"/>
     <usWidthClass value="2"/>
     <fsType value="00000000 00000000"/>
diff --git a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-400,100.ttx b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-400,100.ttx
index c2d205715..635acd719 100644
--- a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-400,100.ttx
+++ b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-400,100.ttx
@@ -74,7 +74,7 @@
     <!-- The fields 'usFirstCharIndex' and 'usLastCharIndex'
          will be recalculated by the compiler -->
     <version value="4"/>
-    <xAvgCharWidth value="577"/>
+    <xAvgCharWidth value="543"/>
     <usWeightClass value="400"/>
     <usWidthClass value="5"/>
     <fsType value="00000000 00000000"/>
diff --git a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-400,62.5.ttx b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-400,62.5.ttx
index 63eeb0e7f..fcafe91c0 100644
--- a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-400,62.5.ttx
+++ b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-400,62.5.ttx
@@ -74,7 +74,7 @@
     <!-- The fields 'usFirstCharIndex' and 'usLastCharIndex'
          will be recalculated by the compiler -->
     <version value="4"/>
-    <xAvgCharWidth value="577"/>
+    <xAvgCharWidth value="428"/>
     <usWeightClass value="400"/>
     <usWidthClass value="2"/>
     <fsType value="00000000 00000000"/>
diff --git a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-900,100.ttx b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-900,100.ttx
index 013ba1e73..61c3b2bb9 100644
--- a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-900,100.ttx
+++ b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-900,100.ttx
@@ -74,7 +74,7 @@
     <!-- The fields 'usFirstCharIndex' and 'usLastCharIndex'
          will be recalculated by the compiler -->
     <version value="4"/>
-    <xAvgCharWidth value="577"/>
+    <xAvgCharWidth value="609"/>
     <usWeightClass value="900"/>
     <usWidthClass value="5"/>
     <fsType value="00000000 00000000"/>
diff --git a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-900,62.5.ttx b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-900,62.5.ttx
index 45e34cbf7..fa31886a6 100644
--- a/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-900,62.5.ttx
+++ b/Tests/varLib/instancer/data/test_results/PartialInstancerTest2-VF-instance-900,62.5.ttx
@@ -74,7 +74,7 @@
     <!-- The fields 'usFirstCharIndex' and 'usLastCharIndex'
          will be recalculated by the compiler -->
     <version value="4"/>
-    <xAvgCharWidth value="577"/>
+    <xAvgCharWidth value="506"/>
     <usWeightClass value="900"/>
     <usWidthClass value="2"/>
     <fsType value="00000000 00000000"/>