diff --git a/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp b/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp
index 326fb0595e06..15c582bc5672 100644
--- a/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp
+++ b/clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp
@@ -84,7 +84,8 @@ void UnusedParametersCheck::warnOnUnusedParameter(
 
   // Fix all redeclarations.
   for (const FunctionDecl *FD : Function->redecls())
-    MyDiag << removeParameter(FD, ParamIndex);
+    if (FD->param_size())
+      MyDiag << removeParameter(FD, ParamIndex);
 
   // Fix all call sites.
   auto CallMatches = ast_matchers::match(
diff --git a/clang-tools-extra/test/clang-tidy/misc-unused-parameters.c b/clang-tools-extra/test/clang-tidy/misc-unused-parameters.c
index 7c1ab34b7b58..1b04ece455b4 100644
--- a/clang-tools-extra/test/clang-tidy/misc-unused-parameters.c
+++ b/clang-tools-extra/test/clang-tidy/misc-unused-parameters.c
@@ -7,6 +7,11 @@ void a(int i) {}
 // CHECK-MESSAGES: :[[@LINE-1]]:12: warning: parameter 'i' is unused [misc-unused-parameters]
 // CHECK-FIXES: {{^}}void a(int  /*i*/) {}{{$}}
 
+static void b(); // In C, forward declarations can leave out parameters.
+static void b(int i) {}
+// CHECK-MESSAGES: :[[@LINE-1]]:19: warning: parameter 'i' is unused [misc-unused-parameters]
+// CHECK-FIXES: {{^}}static void b() {}{{$}}
+
 // Unchanged cases
 // ===============
 void h(i, c, d) int i; char *c, *d; {} // Don't mess with K&R style