diff --git a/src/wtforms/widgets/core.py b/src/wtforms/widgets/core.py
index 5be3f40..4941321 100644
--- a/src/wtforms/widgets/core.py
+++ b/src/wtforms/widgets/core.py
@@ -30,6 +30,10 @@ def html_params(**kwargs):
     name of the attribute begins with ``data_`` or ``aria_``, then every
     underscore will be replaced with a hyphen in the generated attribute.
 
+    If multiple arguments resolve to the same attribute name (e.g. ``class`` and
+    ``class_``), their values will be joined with a space, with ``class_``'s
+    value appended.
+
     >>> html_params(data_attr='user.name', aria_labeledby='name')
     'data-attr="user.name" aria-labeledby="name"'
 
@@ -51,18 +55,42 @@ def html_params(**kwargs):
         ``data_`` args convert all underscores to hyphens, instead of
         only the first one.
     """
-    params = []
-    for k, v in sorted(kwargs.items()):
+    # Normalize parameter names and collect values
+    normalized_params = {}
+    for k, v in kwargs.items():
+        # Convert parameter names
         if k in ("class_", "class__", "for_"):
             k = k[:-1]
         elif k.startswith("data_") or k.startswith("aria_"):
             k = k.replace("_", "-")
+        
+        # Skip False values
+        if v is False:
+            continue
+            
+        # Handle True values (boolean attributes)
         if v is True:
-            params.append(k)
-        elif v is False:
-            pass
+            normalized_params[k] = normalized_params.get(k, []) + [True]
         else:
-            params.append('{}="{}"'.format(str(k), escape(v)))
+            # Collect string values
+            normalized_params[k] = normalized_params.get(k, []) + [str(v)]
+    
+    # Build parameter strings
+    params = []
+    for k in sorted(normalized_params.keys()):
+        values = normalized_params[k]
+        # Filter out True values for special handling
+        true_values = [v for v in values if v is True]
+        str_values = [v for v in values if isinstance(v, str)]
+        
+        if true_values:
+            # Boolean attribute - present if any True value exists
+            params.append(k)
+        elif str_values:
+            # For class attributes, join multiple values with space
+            # For other attributes, join with space as well (consistent behavior)
+            params.append('{}="{}"'.format(k, escape(" ".join(str_values))))
+    
     return " ".join(params)