diff --git a/src/DynareBison.yy b/src/DynareBison.yy
index 78ba1a46..4d6a64f2 100644
--- a/src/DynareBison.yy
+++ b/src/DynareBison.yy
@@ -82,7 +82,7 @@ class ParsingDriver;
 %token COMMA CONSIDER_ALL_ENDOGENOUS CONSIDER_ONLY_OBSERVED INITIAL_CONDITION_DECOMPOSITION
 %token DATAFILE FILE SERIES DOUBLING DR_CYCLE_REDUCTION_TOL DR_LOGARITHMIC_REDUCTION_TOL DR_LOGARITHMIC_REDUCTION_MAXITER DR_ALGO DROP DSAMPLE DYNASAVE DYNATYPE CALIBRATION DIFFERENTIATE_FORWARD_VARS
 %token END ENDVAL EQUAL ESTIMATION ESTIMATED_PARAMS ESTIMATED_PARAMS_BOUNDS ESTIMATED_PARAMS_INIT EXTENDED_PATH ENDOGENOUS_PRIOR EXPRESSION
-%token FILENAME DIRNAME FILTER_STEP_AHEAD FILTERED_VARS FIRST_OBS FIRST_SIMULATION_PERIOD LAST_OBS 
+%token FILENAME DIRNAME FILTER_STEP_AHEAD FILTERED_VARS FIRST_OBS FIRST_SIMULATION_PERIOD LAST_OBS
 %token SET_TIME OSR_PARAMS_BOUNDS KEEP_KALMAN_ALGO_IF_SINGULARITY_IS_DETECTED
 %token <string> FALSE FLOAT_NUMBER DATES
 %token DEFAULT FIXED_POINT FLIP OPT_ALGO COMPILATION_SETUP COMPILER ADD_FLAGS SUBSTITUTE_FLAGS ADD_LIBS SUBSTITUTE_LIBS
@@ -91,6 +91,7 @@ class ParsingDriver;
 %token HISTVAL HISTVAL_FILE HOMOTOPY_SETUP HOMOTOPY_MODE HOMOTOPY_STEPS HOMOTOPY_FORCE_CONTINUE HP_FILTER HP_NGRID FILTERED_THEORETICAL_MOMENTS_GRID HYBRID ONE_SIDED_HP_FILTER
 %token IDENTIFICATION INF_CONSTANT INITVAL INITVAL_FILE BOUNDS JSCALE INIT INFILE INVARS
 %token <string> INT_NUMBER
+%token <string> ZERO
 %token INV_GAMMA_PDF INV_GAMMA1_PDF INV_GAMMA2_PDF IRF IRF_SHOCKS IRF_PLOT_THRESHOLD IRF_CALIBRATION
 %token FAST_KALMAN_FILTER KALMAN_ALGO KALMAN_TOL DIFFUSE_KALMAN_TOL SCHUR_VEC_TOL SUBSAMPLES OPTIONS TOLF TOLX PLOT_INIT_DATE PLOT_END_DATE
 %token LAPLACE LIK_ALGO LIK_INIT LINEAR LINEAR_DECOMPOSITION LOAD_IDENT_FILES LOAD_MH_FILE LOAD_RESULTS_AFTER_LOAD_MH LOAD_PARAMS_AND_STEADY_STATE LOGLINEAR LOGDATA LYAPUNOV LINEAR_APPROXIMATION
@@ -169,8 +170,8 @@ class ParsingDriver;
 %token HETEROSKEDASTIC_FILTER TIME_SHIFT
 /* Method of Moments */
 %token METHOD_OF_MOMENTS MOM_METHOD
-%token BARTLETT_KERNEL_LAG WEIGHTING_MATRIX WEIGHTING_MATRIX_SCALING_FACTOR ANALYTIC_STANDARD_ERRORS ANALYTIC_JACOBIAN PENALIZED_ESTIMATOR VERBOSE 
-%token SIMULATION_MULTIPLE MOM_SEED SEED BOUNDED_SHOCK_SUPPORT ADDITIONAL_OPTIMIZER_STEPS MOM_SE_TOLX SE_TOLX MOM_BURNIN BURNIN 
+%token BARTLETT_KERNEL_LAG WEIGHTING_MATRIX WEIGHTING_MATRIX_SCALING_FACTOR ANALYTIC_STANDARD_ERRORS ANALYTIC_JACOBIAN PENALIZED_ESTIMATOR VERBOSE
+%token SIMULATION_MULTIPLE MOM_SEED SEED BOUNDED_SHOCK_SUPPORT ADDITIONAL_OPTIMIZER_STEPS MOM_SE_TOLX SE_TOLX MOM_BURNIN BURNIN
 %token EQTAGS STEADY_STATE_GROWTH
 %token ANALYTICAL_GIRF IRF_IN_PERCENT EMAS_GIRF EMAS_DROP EMAS_TOLF EMAS_MAX_ITER
 %token NO_IDENTIFICATION_STRENGTH NO_IDENTIFICATION_REDUCEDFORM NO_IDENTIFICATION_MOMENTS
@@ -182,7 +183,7 @@ class ParsingDriver;
 
 %type <expr_t> expression expression_or_empty
 %type <expr_t> equation hand_side
-%type <string> non_negative_number signed_number signed_integer date_str
+%type <string> non_negative_number non_positive_integer signed_number signed_integer date_str
 %type <string> filename symbol namespace_qualified_filename namespace_qualified_symbol
 %type <string> vec_of_vec_value vec_value_list date_expr
 %type <string> vec_value_1 vec_value signed_inf signed_number_w_inf
@@ -449,7 +450,7 @@ var_expectation_model_option : VARIABLE EQUAL symbol
                                { driver.option_str("model_name", $3); }
                              | DISCOUNT EQUAL expression
                                { driver.var_expectation_model_discount = $3; }
-                             | TIME_SHIFT EQUAL signed_integer
+                             | TIME_SHIFT EQUAL non_positive_integer
                                { driver.option_num("time_shift", $3); }
                              ;
 
@@ -1551,6 +1552,14 @@ signed_integer : PLUS INT_NUMBER
                | INT_NUMBER
                ;
 
+non_positive_integer : MINUS INT_NUMBER
+                 {
+                   $$ = $2;
+                   $$.insert(0, "-");
+                 }
+               | ZERO
+               ;
+
 non_negative_number : INT_NUMBER
                     | FLOAT_NUMBER
                     ;
@@ -3822,7 +3831,7 @@ o_analytic_jacobian : ANALYTIC_JACOBIAN { driver.option_num("mom.analytic_jacobi
 o_mom_method : MOM_METHOD EQUAL GMM
                { driver.option_str("mom.mom_method", "GMM"); }
              | MOM_METHOD EQUAL SMM
-               { driver.option_str("mom.mom_method", "SMM"); }                    
+               { driver.option_str("mom.mom_method", "SMM"); }
              ;
 o_penalized_estimator : PENALIZED_ESTIMATOR { driver.option_num("mom.penalized_estimator", "true"); };
 o_verbose : VERBOSE { driver.option_num("mom.verbose", "true"); };
diff --git a/src/DynareFlex.ll b/src/DynareFlex.ll
index 4347d994..69b1c6b1 100644
--- a/src/DynareFlex.ll
+++ b/src/DynareFlex.ll
@@ -947,6 +947,11 @@ DATE -?[0-9]+([ya]|m([1-9]|1[0-2])|q[1-4])
   return token::FLOAT_NUMBER;
 }
 
+<DYNARE_STATEMENT,DYNARE_BLOCK>(0|[-+]0) {
+  yylval->build<string>(yytext);
+  return token::ZERO;
+}
+
 <DYNARE_STATEMENT,DYNARE_BLOCK>[0-9]+ {
   yylval->build<string>(yytext);
   return token::INT_NUMBER;