diff --git a/runtime/scripts/jme-builtins.js b/runtime/scripts/jme-builtins.js
index 6d2b5b7b6..edd9d1b14 100644
--- a/runtime/scripts/jme-builtins.js
+++ b/runtime/scripts/jme-builtins.js
@@ -979,10 +979,10 @@ newBuiltin('-u', [TDecimal], TDecimal, function(a){ return a.negated(); });
 newBuiltin('+', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.plus(b); });
 newBuiltin('+', [TNum,TDecimal], TDecimal, function(a,b){ return math.ensure_decimal(a).plus(b); });
 newBuiltin('-', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.minus(b); });
-newBuiltin('-', [TNum,TDecimal], TDecimal, function(a,b){ return (new math.ComplexDecimal(new Decimal(a))).minus(b); });
+newBuiltin('-', [TNum,TDecimal], TDecimal, function(a,b){ return math.ensure_decimal(a).minus(b); });
 newBuiltin('*', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.times(b); });
 newBuiltin('/', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.dividedBy(b); });
-newBuiltin('/', [TNum,TDecimal], TDecimal, function(a,b){ return (new math.ComplexDecimal(new Decimal(a))).dividedBy(b); });
+newBuiltin('/', [TNum,TDecimal], TDecimal, function(a,b){ return math.ensure_decimal(a).dividedBy(b); });
 newBuiltin('abs', [TDecimal], TDecimal, function(a){ return a.absoluteValue(); });
 newBuiltin('ceil', [TDecimal], TDecimal, function(a){ return a.re.ceil(); });
 newBuiltin('cos', [TDecimal], TDecimal, function(a){ return a.re.cos(); });
@@ -1032,7 +1032,7 @@ newBuiltin('min', [sig.listof(sig.type('decimal'))], TDecimal, function(l) { ret
 newBuiltin('dpformat',[TDecimal,TNum], TString, function(a,dp) {return a.toFixed(dp); });
 newBuiltin('tonearest',[TDecimal,TDecimal], TDecimal, function(a,x) {return a.toNearest(x.re); });
 newBuiltin('^',[TDecimal,TDecimal], TDecimal, function(a,b) {return a.pow(b); });
-newBuiltin('^', [TInt,TDecimal], TDecimal, function(a,b) { return (new math.ComplexDecimal(math.numberToDecimal(a))).pow(b); });
+newBuiltin('^', [TInt,TDecimal], TDecimal, function(a,b) { return math.ensure_decimal(a).pow(b); });
 newBuiltin('sigformat',[TDecimal,TNum], TString, function(a,sf) {return a.toPrecision(sf); });
 function_with_precision_info('siground', function(a,dp) {return a.toSignificantDigits(dp); }, TDecimal, 'sigfig');
 newBuiltin('formatnumber', [TDecimal,TString], TString, function(n,style) {return math.niceComplexDecimal(n,{style:style});});
diff --git a/tests/jme-runtime.js b/tests/jme-runtime.js
index 09879edec..8e7c46dfb 100644
--- a/tests/jme-runtime.js
+++ b/tests/jme-runtime.js
@@ -2697,9 +2697,11 @@ var math = Numbas.math = /** @lends Numbas.math */ {
         }
         rel_tol = rel_tol===undefined ? 1e-15 : rel_tol;
         abs_tol = abs_tol===undefined ? 1e-15: abs_tol;
+
         if(a.complex || b.complex) {
             return math.abs(math.sub(a,b)) < abs_tol;
         }
+
         return Math.abs(a-b) <= Math.max( rel_tol * Math.max(Math.abs(a), Math.abs(b)), abs_tol );
     },
 
@@ -14110,10 +14112,10 @@ newBuiltin('-u', [TDecimal], TDecimal, function(a){ return a.negated(); });
 newBuiltin('+', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.plus(b); });
 newBuiltin('+', [TNum,TDecimal], TDecimal, function(a,b){ return math.ensure_decimal(a).plus(b); });
 newBuiltin('-', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.minus(b); });
-newBuiltin('-', [TNum,TDecimal], TDecimal, function(a,b){ return (new math.ComplexDecimal(new Decimal(a))).minus(b); });
+newBuiltin('-', [TNum,TDecimal], TDecimal, function(a,b){ return math.ensure_decimal(a).minus(b); });
 newBuiltin('*', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.times(b); });
 newBuiltin('/', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.dividedBy(b); });
-newBuiltin('/', [TNum,TDecimal], TDecimal, function(a,b){ return (new math.ComplexDecimal(new Decimal(a))).dividedBy(b); });
+newBuiltin('/', [TNum,TDecimal], TDecimal, function(a,b){ return math.ensure_decimal(a).dividedBy(b); });
 newBuiltin('abs', [TDecimal], TDecimal, function(a){ return a.absoluteValue(); });
 newBuiltin('ceil', [TDecimal], TDecimal, function(a){ return a.re.ceil(); });
 newBuiltin('cos', [TDecimal], TDecimal, function(a){ return a.re.cos(); });
@@ -14163,7 +14165,7 @@ newBuiltin('min', [sig.listof(sig.type('decimal'))], TDecimal, function(l) { ret
 newBuiltin('dpformat',[TDecimal,TNum], TString, function(a,dp) {return a.toFixed(dp); });
 newBuiltin('tonearest',[TDecimal,TDecimal], TDecimal, function(a,x) {return a.toNearest(x.re); });
 newBuiltin('^',[TDecimal,TDecimal], TDecimal, function(a,b) {return a.pow(b); });
-newBuiltin('^', [TInt,TDecimal], TDecimal, function(a,b) { return (new math.ComplexDecimal(math.numberToDecimal(a))).pow(b); });
+newBuiltin('^', [TInt,TDecimal], TDecimal, function(a,b) { return math.ensure_decimal(a).pow(b); });
 newBuiltin('sigformat',[TDecimal,TNum], TString, function(a,sf) {return a.toPrecision(sf); });
 function_with_precision_info('siground', function(a,dp) {return a.toSignificantDigits(dp); }, TDecimal, 'sigfig');
 newBuiltin('formatnumber', [TDecimal,TString], TString, function(n,style) {return math.niceComplexDecimal(n,{style:style});});
diff --git a/tests/jme/jme-tests.mjs b/tests/jme/jme-tests.mjs
index 0743f28c3..30784b150 100644
--- a/tests/jme/jme-tests.mjs
+++ b/tests/jme/jme-tests.mjs
@@ -660,6 +660,7 @@ Numbas.queueScript('jme_tests',['qunit','jme','jme-rules','jme-display','jme-cal
         assert.notOk(Numbas.jme.builtinScope.evaluate('iszero(dec(pi)-arccos(-1))').value,'dec(pi) uses more accurate pi than Math.PI');
         deepCloseEqual(assert, evaluateNumber('dec(1+2i)/dec(3+4i)'),math.complex(11/25,2/25),'dec(1+2i)/(3+4i)');
         deepCloseEqual(assert, Numbas.jme.builtinScope.evaluate('(1+2i)+dec(3)').value,new math.ComplexDecimal(new Decimal(4),new Decimal(2)),'(1+2i)+dec(3)');
+        deepCloseEqual(assert, evaluate('i - dec(1)').value, new math.ComplexDecimal(new Decimal(-1), new Decimal(1)), 'i - dec(1)');
 
         for(let a of [1,-1,2,-2,9,-9]) {
             for(let b of [0,1,-1,2,-2,0.5,-0.5,1.5,-0.5,3,-3]) {
diff --git a/tests/numbas-runtime.js b/tests/numbas-runtime.js
index 13d315bfc..d03833ceb 100644
--- a/tests/numbas-runtime.js
+++ b/tests/numbas-runtime.js
@@ -2698,9 +2698,11 @@ var math = Numbas.math = /** @lends Numbas.math */ {
         }
         rel_tol = rel_tol===undefined ? 1e-15 : rel_tol;
         abs_tol = abs_tol===undefined ? 1e-15: abs_tol;
+
         if(a.complex || b.complex) {
             return math.abs(math.sub(a,b)) < abs_tol;
         }
+
         return Math.abs(a-b) <= Math.max( rel_tol * Math.max(Math.abs(a), Math.abs(b)), abs_tol );
     },
 
@@ -14098,10 +14100,10 @@ newBuiltin('-u', [TDecimal], TDecimal, function(a){ return a.negated(); });
 newBuiltin('+', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.plus(b); });
 newBuiltin('+', [TNum,TDecimal], TDecimal, function(a,b){ return math.ensure_decimal(a).plus(b); });
 newBuiltin('-', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.minus(b); });
-newBuiltin('-', [TNum,TDecimal], TDecimal, function(a,b){ return (new math.ComplexDecimal(new Decimal(a))).minus(b); });
+newBuiltin('-', [TNum,TDecimal], TDecimal, function(a,b){ return math.ensure_decimal(a).minus(b); });
 newBuiltin('*', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.times(b); });
 newBuiltin('/', [TDecimal,TDecimal], TDecimal, function(a,b){ return a.dividedBy(b); });
-newBuiltin('/', [TNum,TDecimal], TDecimal, function(a,b){ return (new math.ComplexDecimal(new Decimal(a))).dividedBy(b); });
+newBuiltin('/', [TNum,TDecimal], TDecimal, function(a,b){ return math.ensure_decimal(a).dividedBy(b); });
 newBuiltin('abs', [TDecimal], TDecimal, function(a){ return a.absoluteValue(); });
 newBuiltin('ceil', [TDecimal], TDecimal, function(a){ return a.re.ceil(); });
 newBuiltin('cos', [TDecimal], TDecimal, function(a){ return a.re.cos(); });
@@ -14151,7 +14153,7 @@ newBuiltin('min', [sig.listof(sig.type('decimal'))], TDecimal, function(l) { ret
 newBuiltin('dpformat',[TDecimal,TNum], TString, function(a,dp) {return a.toFixed(dp); });
 newBuiltin('tonearest',[TDecimal,TDecimal], TDecimal, function(a,x) {return a.toNearest(x.re); });
 newBuiltin('^',[TDecimal,TDecimal], TDecimal, function(a,b) {return a.pow(b); });
-newBuiltin('^', [TInt,TDecimal], TDecimal, function(a,b) { return (new math.ComplexDecimal(math.numberToDecimal(a))).pow(b); });
+newBuiltin('^', [TInt,TDecimal], TDecimal, function(a,b) { return math.ensure_decimal(a).pow(b); });
 newBuiltin('sigformat',[TDecimal,TNum], TString, function(a,sf) {return a.toPrecision(sf); });
 function_with_precision_info('siground', function(a,dp) {return a.toSignificantDigits(dp); }, TDecimal, 'sigfig');
 newBuiltin('formatnumber', [TDecimal,TString], TString, function(n,style) {return math.niceComplexDecimal(n,{style:style});});