diff --git a/src/librustc_trans/builder.rs b/src/librustc_trans/builder.rs
index 66ae60345c50..4615a3b17c61 100644
--- a/src/librustc_trans/builder.rs
+++ b/src/librustc_trans/builder.rs
@@ -914,7 +914,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         self.count_insn("minnum");
         unsafe {
             let instr = llvm::LLVMRustBuildMinNum(self.llbuilder, lhs, rhs);
-            bug!("LLVMRustBuildMinNum is not available in LLVM version < 6.0");
+            if instr.is_null() {
+                bug!("LLVMRustBuildMinNum is not available in LLVM version < 6.0");
+            }
             instr
         }
     }
@@ -922,7 +924,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         self.count_insn("maxnum");
         unsafe {
             let instr = llvm::LLVMRustBuildMaxNum(self.llbuilder, lhs, rhs);
-            bug!("LLVMRustBuildMaxNum is not available in LLVM version < 6.0");
+            if instr.is_null() {
+                bug!("LLVMRustBuildMaxNum is not available in LLVM version < 6.0");
+            }
             instr
         }
     }