diff --git a/src/V3Life.cpp b/src/V3Life.cpp
index 5b0c45921..a34493aa2 100644
--- a/src/V3Life.cpp
+++ b/src/V3Life.cpp
@@ -304,6 +304,7 @@ private:
         AstVarScope* vscp = nodep->varScopep();
         if (!vscp) nodep->v3fatalSrc("Scope not assigned");
         if (nodep->lvalue()) {
+            m_sideEffect = true;  // $sscanf etc may have RHS vars that are lvalues
             m_lifep->complexAssign(vscp);
         } else {
             m_lifep->varUsageReplace(vscp, nodep); VL_DANGLING(nodep);
diff --git a/test_regress/t/t_sys_file_basic.v b/test_regress/t/t_sys_file_basic.v
index 5ec60a216..c4fc6f097 100644
--- a/test_regress/t/t_sys_file_basic.v
+++ b/test_regress/t/t_sys_file_basic.v
@@ -6,6 +6,8 @@
 `include "verilated.v"
 
 `define STRINGIFY(x) `"x`"
+`define ratio_error(a,b) (((a)>(b) ? ((a)-(b)) : ((b)-(a))) /(a))
+`define checkr(gotv,expv) do if (`ratio_error((gotv),(expv))>0.0001) begin $write("%%Error: %s:%0d:  got=%g exp=%g\n", `__FILE__,`__LINE__, (gotv), (expv)); $stop; end while(0);
 
 module t;
    integer file;
@@ -113,12 +115,12 @@ module t;
 	 if (chars != 1) $stop;
 	 if (letterq != "ijklmnop") $stop;
 
-	 chars = $sscanf("xa=1f xb=12898971238912389712783490823_237904689_02348923",
+	 chars = $sscanf("xa=1f xb=12898971238912389712783490823_abcdef689_02348923",
 			 "xa=%x xb=%x", letterq, letterw);
 	 if (`verbose) $write("c=%0d xa=%x xb=%x\n", chars, letterq, letterw);
 	 if (chars != 2) $stop;
 	 if (letterq != 64'h1f) $stop;
-	 if (letterw != 128'h38971278349082323790468902348923) $stop;
+	 if (letterw != 128'h389712783490823_abcdef689_02348923) $stop;
 
 	 chars = $sscanf("ba=10      bb=110100101010010101012    note_the_two ",
 			 "ba=%b bb=%b%s", letterq, letterw, letterz);
@@ -139,14 +141,25 @@ module t;
 			 "r=%g d=%d", r, letterq);
 	 if (`verbose) $write("c=%0d d=%d\n", chars, letterq);
 	 if (chars != 2) $stop;
-	 if (r != 0.1) $stop;
+	 `checkr(r, 0.1);
 	 if (letterq != 64'hfffffffffffc65a5) $stop;
 
+	 // Cover quad and %e/%f
+	 chars = $sscanf("r=0.2",
+			 "r=%e", r);
+	 if (`verbose) $write("c=%0d r=%e\n", chars, r);
+	 `checkr(r, 0.2);
+
+	 chars = $sscanf("r=0.3",
+			 "r=%f", r);
+	 if (`verbose) $write("c=%0d r=%f\n", chars, r);
+	 `checkr(r, 0.3);
+
 	 s = "r=0.2 d=-236124";
 	 chars = $sscanf(s, "r=%g d=%d", r, letterq);
 	 if (`verbose) $write("c=%0d d=%d\n", chars, letterq);
 	 if (chars != 2) $stop;
-	 if (r != 0.2) $stop;
+	 `checkr(r, 0.2);
 	 if (letterq != 64'hfffffffffffc65a4) $stop;
 
 	 // $fscanf