diff --git a/Lib/fontTools/varLib/featureVars.py b/Lib/fontTools/varLib/featureVars.py
index 856f00bcb9..40ad9dfca6 100644
--- a/Lib/fontTools/varLib/featureVars.py
+++ b/Lib/fontTools/varLib/featureVars.py
@@ -95,6 +95,14 @@ def addFeatureVariations(font, conditionalSubstitutions, featureTag="rvrn"):
 
     addFeatureVariationsRaw(font, font["GSUB"].table, conditionsAndLookups, featureTags)
 
+    # Update OS/2.usMaxContext in case the font didn't have features before, but
+    # does now, if the OS/2 table exists. The table may be required, but
+    # fontTools needs to be able to deal with non-standard fonts. Since feature
+    # variations are always 1:1 mappings, we can set the value to at least 1
+    # instead of recomputing it with `otlLib.maxContextCalc.maxCtxFont()`.
+    if (os2 := font.get("OS/2")) is not None:
+        os2.usMaxContext = max(1, os2.usMaxContext)
+
 
 def _existingVariableFeatures(table):
     existingFeatureVarsTags = set()
diff --git a/Tests/varLib/featureVars_test.py b/Tests/varLib/featureVars_test.py
index ef32ee0315..a7d7213d83 100644
--- a/Tests/varLib/featureVars_test.py
+++ b/Tests/varLib/featureVars_test.py
@@ -21,6 +21,8 @@ def makeVariableFont(glyphOrder, axes):
         axis.minimum, axis.default, axis.maximum = minimum, default, maximum
         ds_axes[axisTag] = axis
     varLib._add_fvar(font, ds_axes, instances=())
+    os2 = font["OS/2"] = newTable("OS/2")
+    os2.usMaxContext = 0
     return font
 
 
@@ -35,7 +37,9 @@ def varfont():
 def test_addFeatureVariations(varfont):
     assert "GSUB" not in varfont
 
+    assert varfont["OS/2"].usMaxContext == 0
     addFeatureVariations(varfont, [([{"wght": (0.5, 1.0)}], {"A": "A.alt"})])
+    assert varfont["OS/2"].usMaxContext == 1
 
     assert "GSUB" in varfont
     gsub = varfont["GSUB"].table